Document and Entity Information	6 Months Ended
Document and Entity Information	Jun. 30, 2015	Aug. 06, 2015
Document and Entity Information [Abstract]
Entity Registrant Name	KIRBY CORP
Entity Central Index Key	0000056047
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		54,778,000
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2015

CONDENSED BALANCE SHEETS (Unaudited) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 4,989	$ 24,299
Accounts receivable:
Trade - less allowance for doubtful accounts	337,011	417,325
Other	92,582	115,598
Inventories - net	191,061	192,354
Prepaid expenses and other current assets	38,139	43,016
Deferred income taxes	12,844	10,562
Total current assets	676,626	803,154
Property and equipment	3,942,527	3,717,398
Less accumulated depreciation	(1,210,868)	(1,127,900)
Property and equipment - net	2,731,659	2,589,498
Goodwill	591,405	591,405
Other assets	154,813	157,852
Total assets	4,154,503	4,141,909
Current liabilities:
Current portion of long-term debt	0	116,700
Income taxes payable	1,106	3,470
Accounts payable	162,426	222,020
Accrued liabilities	180,946	201,033
Deferred revenues	43,311	50,804
Total current liabilities	387,789	594,027
Long-term debt - less current portion	808,300	600,000
Deferred income taxes	614,065	595,769
Other long-term liabilities	88,506	87,200
Total long-term liabilities	1,510,871	1,282,969
Contingencies and commitments
Kirby stockholders' equity:
Common stock, $.10 par value per share. Authorized 120,000,000 shares, issued 59,776,000 shares	5,978	5,978
Additional paid-in capital	428,835	428,475
Accumulated other comprehensive income - net	(57,439)	(61,037)
Retained earnings	2,093,299	1,974,146
Treasury stock - at cost, 4,517,000 at June 30, 2015 and 2,906,000 at December 31, 2014	(225,636)	(93,526)
Total Kirby stockholders' equity	2,245,037	2,254,036
Noncontrolling interests	10,806	10,877
Total equity	2,255,843	2,264,913
Total liabilities and equity	$ 4,154,503	$ 4,141,909

CONDENSED BALANCE SHEETS (Unaudited) (Parenthetical) (USD $)	Jun. 30, 2015	Dec. 31, 2014
Equity:
Common stock, par value per share (in dollars per share)	$ 0.10	$ 0.10
Common stock, shares authorized (in shares)	120,000,000	120,000,000
Common stock, shares issued (in shares)	59,776,000	59,776,000
Treasury stock, shares (in shares)	4,517,000	2,906,000

CONDENSED STATEMENTS OF EARNINGS (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Revenues:
Marine transportation	$ 425,053	$ 456,745	$ 844,958	$ 892,516
Diesel engine services	118,103	171,309	285,871	324,784
Total revenues	543,156	628,054	1,130,829	1,217,300
Costs and expenses:
Costs of sales and operating expenses	343,745	403,460	728,526	786,689
Selling, general and administrative	49,165	52,065	100,209	105,663
Taxes, other than on income	5,378	4,624	9,923	9,204
Depreciation and amortization	46,825	41,407	92,591	82,443
Gain on disposition of assets	(91)	(527)	(1,646)	(578)
Total costs and expenses	445,022	501,029	929,603	983,421
Operating income	98,134	127,025	201,226	233,879
Other income (expense)	(303)	123	(243)	(113)
Interest expense	(4,759)	(5,469)	(10,009)	(11,087)
Earnings before taxes on income	93,072	121,679	190,974	222,679
Provision for taxes on income	(34,696)	(45,768)	(71,187)	(83,757)
Net earnings	58,376	75,911	119,787	138,922
Less: Net earnings attributable to noncontrolling interests	(301)	(919)	(634)	(1,684)
Net earnings attributable to Kirby	$ 58,075	$ 74,992	$ 119,153	$ 137,238
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.04	$ 1.32	$ 2.14	$ 2.41
Diluted (in dollars per share)	$ 1.04	$ 1.31	$ 2.13	$ 2.40

CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
CONDENSED STATEMENTS OF COMPREHENSIVE INCOME (Unaudited) [Abstract]
Net earnings	$ 58,376	$ 75,911	$ 119,787	$ 138,922
Other comprehensive income (loss), net of taxes:
Pension and postretirement benefits	2,458	444	3,566	468
Foreign currency translation adjustments	129	9	32	(8)
Change in fair value of derivative instruments	0	0	0	84
Total comprehensive income, net of taxes	2,587	453	3,598	544
Total comprehensive income, net of taxes	60,963	76,364	123,385	139,466
Net earnings attributable to noncontrolling interests	(301)	(919)	(634)	(1,684)
Comprehensive income attributable to Kirby	$ 60,662	$ 75,445	$ 122,751	$ 137,782

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014
Cash flows from operating activities:
Net earnings	$ 119,787	$ 138,922
Adjustments to reconcile net earnings to net cash provided by operations:
Depreciation and amortization	92,591	82,443
Provision for deferred income taxes	13,801	14,413
Amortization of unearned share-based compensation	5,251	5,273
Amortization of major maintenance costs	10,360	7,713
Other	70	(574)
Increase in cash flows resulting from changes in operating assets and liabilities, net	4,058	3,218
Net cash provided by operating activities	245,918	251,408
Cash flows from investing activities:
Capital expenditures	(190,152)	(163,299)
Acquisition of marine equipment	(41,250)	0
Proceeds from disposition of assets	10,636	3,884
Net cash used in investing activities	(220,766)	(159,415)
Cash flows from financing activities:
Borrowings (payments) on bank credit facilities, net	190,321	(33,850)
Payments on long-term debt	(100,000)	(66,000)
Proceeds from exercise of stock options	3,712	7,275
Purchase of treasury stock	(138,851)	0
Payment of contingent liability	0	(4,756)
Excess tax benefit from equity compensation plans	1,064	6,155
Other	(708)	(1,905)
Net cash used in financing activities	(44,462)	(93,081)
Decrease in cash and cash equivalents	(19,310)	(1,088)
Cash and cash equivalents, beginning of year	24,299	4,022
Cash and cash equivalents, end of period	4,989	2,934
Cash paid during the period:
Interest	10,550	9,960
Income taxes	$ 45,360	$ 58,632

ACCOUNTING STANDARDS ADOPTIONS

6 Months Ended

Jun. 30, 2015

ACCOUNTING STANDARDS ADOPTIONS [Abstract]

ACCOUNTING STANDARDS ADOPTIONS

(2)	ACCOUNTING STANDARDS ADOPTIONS

In July 2015, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2015-11, "Inventory (Topic 330): Simplifying the Measurement of Inventory" (“ASU 2015-11”) which applies to inventory that is measured using first-in, first-out ("FIFO") or average cost. Under the guidance, an entity should measure inventory that is within the scope of this update at the lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. Subsequent measurement is unchanged for inventory that is measured using last-in, last-out ("LIFO") or the retail inventory method. ASU 2015-11 is effective for annual and interim periods beginning after December 15, 2016, and should be applied prospectively with early adoption permitted at the beginning of an interim or annual reporting period. The Company is currently evaluating the impact of adopting this guidance.

In April 2015, the FASB issued ASU 2015-03, “Simplifying the Presentation of Debt Issuance Costs” (“ASU 2015-03”). ASU 2015-03 requires debt issuance costs to be presented in the balance sheet as a direct deduction from the associated debt liability. ASU 2015-03 is effective for the Company for financial statements issued for fiscal years beginning after December 15, 2015, and interim periods within those fiscal years. Early adoption is permitted for financial statements that have not been previously issued. The Company will adopt the standard in the first quarter of 2016 and does not expect the effect of ASU 2015-03 to have a material impact on the Company’s consolidated financial statements.

In May 2014, the FASB issued ASU 2014-09, “Revenue from Contracts with Customers” (“ASU 2014-09”). ASU 2014-09 requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. ASU 2014-09 will replace most existing revenue recognition guidance in United States Generally Accepted Accounting Principles when it becomes effective. In July 2015, the FASB voted to delay the effective date of ASU 2014-09 by one year, making it effective for fiscal years, and interim periods within those years, beginning after December 15, 2017 with early adoption permitted as of the original effective date. ASU 2014-09 permits the use of either the retrospective or cumulative effect transition method. The Company is evaluating the effect that ASU 2014-09 will have on its consolidated financial statements and related disclosures. The Company has not yet selected a transition method nor has it determined the effect of ASU 2014-09 on its ongoing financial reporting.

STOCK AWARD PLANS

6 Months Ended

Jun. 30, 2015

STOCK AWARD PLANS [Abstract]

STOCK AWARD PLANS

(5)	STOCK AWARD PLANS

The Company has share-based compensation plans which are described below. The compensation cost that has been charged against earnings for the Company’s stock award plans and the income tax benefit recognized in the statement of earnings for stock awards for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
Compensation cost		$	2,713		$	3,120		$	5,251		$	5,273
Income tax benefit		$	1,015		$	1,182		$	1,964		$	1,998

The Company has an employee stock award plan for selected officers and other key employees which provides for the issuance of stock options, restricted stock and performance awards. The exercise price for each option equals the fair market value per share of the Company’s common stock on the date of grant. The options have seven year terms and vest ratably over three years. No performance awards payable in stock have been awarded under the plan. At June 30, 2015, 2,321,347 shares were available for future grants under the employee plan and no outstanding stock options under the employee plan were issued with stock appreciation rights.

The following is a summary of the stock option activity under the employee plan described above for the six months ended June 30, 2015:

	Outstanding Non- Qualified or Nonincentive Stock Awards			Weighted Average Exercise Price
Outstanding at December 31, 2014		322,956		$	69.95
Granted		114,894		$	74.99
Exercised		─			─
Forfeited		(7,418	)	$	86.28
Outstanding at June 30, 2015		430,432		$	71.01

The following table summarizes information about the Company’s outstanding and exercisable stock options under the employee plan at June 30, 2015:

		Options Outstanding							Options Exercisable
Range of Exercise Prices		Number Outstanding		Weighted Average Remaining Contractual Life in Years		Weighted Average Exercise Price		Aggregate Intrinsic Value	Number Exercisable		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	31.35 - $ 36.35		16,910		1.6	$	32.82			16,910	$	32.82
$	46.74		56,629		2.6	$	46.74			56,629	$	46.74
$	65.28 - $ 74.99		283,963		5.1	$	70.98			141,669	$	67.90
$	93.64 - $ 96.85		35,763		5.6	$	94.27			11,921	$	94.27
$	101.46 -$114.11		37,167		5.7	$	103.22			12,389	$	103.22
$	31.35 -$114.11		430,432		4.7	$	71.01	$4,047,000		239,518	$	63.56	$3,677,000

The following is a summary of the restricted stock award activity under the employee plan described above for the six months ended June 30, 2015:

	Unvested Restricted Stock Award Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested balance at December 31, 2014		321,453		$	71.04
Granted		122,740		$	75.04
Vested		(113,470	)	$	60.75
Forfeited		(10,617	)	$	85.45
Nonvested balance at June 30, 2015		320,106		$	75.74

The Company has a stock award plan for nonemployee directors of the Company which provides for the issuance of stock options and restricted stock. The director plan provides for automatic grants of restricted stock to nonemployee directors after each annual meeting of stockholders. In addition, the director plan allows for the issuance of stock options or restricted stock in lieu of cash for all or part of the annual director fee at the option of the director. The exercise prices for all options granted under the plan are equal to the fair market value per share of the Company’s common stock on the date of grant. The terms of the options are ten years. The restricted stock issued after each annual meeting of stockholders vests six months after the date of grant. Options granted and restricted stock issued in lieu of cash director fees vest in equal quarterly increments during the year to which they relate. At June 30, 2015, 541,038 shares were available for future grants under the director plan. The director stock award plan is intended as an incentive to attract and retain qualified independent directors.

The following is a summary of the stock option activity under the director plan described above for the six months ended June 30, 2015:

	Outstanding Non- Qualified or Nonincentive Stock Options			Weighted Average Exercise Price
Outstanding at December 31, 2014	298,334		$	60.01
Granted	─		$	─
Exercised	(77,905	)	$	47.65
Outstanding at June 30, 2015	220,429		$	64.37

The following table summarizes information about the Company’s outstanding and exercisable stock options under the director plan at June 30, 2015:

		Options Outstanding							Options Exercisable
Range of Exercise Prices		Number Outstanding		Weighted Average Remaining Contractual Life in Years		Weighted Average Exercise Price		Aggregate Intrinsic Value	Number Exercisable		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	29.60 - $36.82		30,000		2.4	$	33.60			30,000	$	33.60
$	41.24 - $56.45		71,276		4.8	$	52.34			71,276	$	52.34
$	61.89 - $62.48		41,153		7.0	$	62.34			41,153	$	62.34
$	75.17 - $99.52		78,000		7.8	$	88.28			78,000	$	88.28
$	29.60 - $99.52		220,429		5.9	$	64.37	$3,668,000		220,429	$	64.37	$3,668,000

The following is a summary of the restricted stock award activity under the director plan described above for the six months ended June 30, 2015:

	Unvested Restricted Stock Award Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested balance at December 31, 2014		292		$	99.52
Granted		18,843		$	79.46
Vested		(575	)	$	89.65
Nonvested balance at June 30, 2015		18,560		$	79.46

The total intrinsic value of all stock options exercised under all of the Company’s plans was $2,555,000 and $11,456,000 for the six months ended June 30, 2015 and 2014, respectively. The actual tax benefit realized for tax deductions from stock option exercises was $956,000 and $4,342,000 for the six months ended June 30, 2015 and 2014, respectively.

The total intrinsic value of all the restricted stock vestings under all of the Company’s plans was $9,015,000 and $13,949,000 for the six months ended June 30, 2015 and 2014, respectively. The actual tax benefit realized for tax deductions from restricted stock vestings was $3,372,000 and $5,287,000 for the six months ended June 30, 2015 and 2014, respectively.

As of June 30, 2015, there was $4,204,000 of unrecognized compensation cost related to nonvested stock options and $22,036,000 related to restricted stock. The stock options are expected to be recognized over a weighted average period of approximately 1.7 years and restricted stock over approximately 3.2 years. The total fair value of options vested was $2,194,000 and $2,076,000 during the six months ended June 30, 2015 and 2014, respectively. The fair value of the restricted stock vested was $9,015,000 and $13,949,000 for the six months ended June 30, 2015 and 2014, respectively.

The weighted average per share fair value of stock options granted during the six months ended June 30, 2015 and 2014 was $25.18 and $36.05, respectively. The fair value of the stock options granted during the six months ended June 30, 2015 and 2014 was $2,893,000 and $4,226,000, respectively. The Company currently uses treasury stock shares for restricted stock grants and stock option exercises. The fair value of each stock option was determined using the Black-Scholes option pricing model. The key input variables used in valuing the options during the six months ended June 30, 2015 and 2014 were as follows:

	Six months ended June 30,
	2015		2014
Dividend yield	None		None
Average risk-free interest rate		1.3%		2.0%
Stock price volatility		33%		33%
Estimated option term	Six years		Six or seven years

OTHER COMPREHENSIVE INCOME

6 Months Ended

Jun. 30, 2015

OTHER COMPREHENSIVE INCOME [Abstract]

OTHER COMPREHENSIVE INCOME

(6) OTHER COMPREHENSIVE INCOME

The Company’s changes in other comprehensive income for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Three months ended June 30,
	2015										2014
	Gross Amount			Income Tax (Provision) Benefit				Net Amount			Gross Amount				Income Tax (Provision) Benefit				Net Amount

Pension and postretirement benefits (a):
Amortization of net actuarial loss		$	1,688		$	(642	)		$	1,046		$	(2	)		$	—			$	(2	)
Actuarial gains			2,293			(881	)			1,412			721				(275	)			446
Foreign currency translation adjustments			129			—				129			9				—				9
Change in fair value of derivative instruments (b):
Reclassified to net earnings			—			—				—			—				—				—
Total		$	4,110		$	(1,523	)		$	2,587		$	728			$	(275	)		$	453

	Six months ended June 30,
	2015										2014
	Gross Amount			Income Tax (Provision) Benefit				Net Amount			Gross Amount				Income Tax (Provision) Benefit				Net Amount

Pension and postretirement benefits (a):
Amortization of net actuarial loss		$	3,486		$	(1,332	)		$	2,154		$	35			$	(13	)		$	22
Actuarial gains			2,293			(881	)			1,412			721				(275	)			446
Foreign currency translation adjustments			32			—				32			(8	)			—				(8	)
Change in fair value of derivative instruments (b):
Reclassified to net earnings			—			—				—			146				(62	)			84
Total		$	5,811		$	(2,213	)		$	3,598		$	894			$	(350	)		$	544

(a)

Actuarial gains (losses) are amortized into costs of sales and operating expenses or selling, general and administrative expenses as appropriate. (See Note 10 – Retirement Plans)

(b)

Reclassifications to net earnings of derivatives qualifying as effective hedges are recognized in costs of sales and operating expenses.

SEGMENT DATA

6 Months Ended

Jun. 30, 2015

SEGMENT DATA [Abstract]

SEGMENT DATA

(7)	SEGMENT DATA

The Company’s operations are classified into two reportable business segments as follows:

Marine Transportation — Provides marine transportation principally by United States flag vessels of liquid cargoes throughout the United States inland waterway system, along all three United States coasts, in Alaska and Hawaii and, to a lesser extent, in United States coastal transportation of dry-bulk cargoes. The principal products transported include petrochemicals, black oil, refined petroleum products and agricultural chemicals.

Diesel Engine Services — Provides after-market services for medium-speed and high-speed diesel engines, reduction gears and ancillary products for marine and power generation applications, distributes and services high-speed diesel engines, transmissions, pumps and compression products, and manufactures and remanufactures oilfield service equipment, including pressure pumping units, for the land-based pressure pumping and oilfield service markets.

The Company’s two reportable business segments are managed separately based on fundamental differences in their operations. The Company evaluates the performance of its segments based on the contributions to operating income of the respective segments, and before income taxes, interest, gains or losses on disposition of assets, other nonoperating income, noncontrolling interests, accounting changes, and nonrecurring items. Intersegment sales for the three months and six months ended June 30, 2015 and 2014 were not significant.

The following table sets forth the Company’s revenues and profit or loss by reportable segment for the three months and six months ended June 30, 2015 and 2014 and total assets as of June 30, 2015 and December 31, 2014 (in thousands):

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
Revenues:
Marine transportation	$	425,053		$	456,745		$	844,958		$	892,516
Diesel engine services		118,103			171,309			285,871			324,784
	$	543,156		$	628,054		$	1,130,829		$	1,217,300
Segment profit (loss):
Marine transportation	$	97,011		$	115,968		$	193,280		$	213,519
Diesel engine services		4,931			14,337			13,774			27,109
Other		(8,870	)		(8,626	)		(16,080	)		(17,949	)
	$	93,072		$	121,679		$	190,974		$	222,679

	June 30, 2015		December 31, 2014
Total assets:
Marine transportation	$	3,425,973	$	3,317,696
Diesel engine services		673,675		736,129
Other		54,855		88,084
	$	4,154,503	$	4,141,909

The following table presents the details of “Other” segment loss for the three months and six months ended June 30, 2015 and 2014 (in thousands):

	Three months ended June 30,								Six months ended June 30,
	2015				2014				2015				2014

General corporate expenses		$	(3,899	)		$	(3,807	)		$	(7,474	)		$	(7,327	)
Gain on disposition of assets			91				527				1,646				578
Interest expense			(4,759	)			(5,469	)			(10,009	)			(11,087	)
Other income (expense)			(303	)			123				(243	)			(113	)
		$	(8,870	)		$	(8,626	)		$	(16,080	)		$	(17,949	)

The following table presents the details of “Other” total assets as of June 30, 2015 and December 31, 2014 (in thousands):

	June 30, 2015		December 31, 2014
General corporate assets	$	52,983	$	85,545
Investment in affiliates		1,872		2,539
	$	54,855	$	88,084

EARNINGS PER SHARE

6 Months Ended

Jun. 30, 2015

EARNINGS PER SHARE [Abstract]

EARNINGS PER SHARE

(9)	EARNINGS PER SHARE

The following table presents the components of basic and diluted earnings per share of common stock for the three months and six months ended June 30, 2015 and 2014 (in thousands, except per share amounts):

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014

Net earnings attributable to Kirby	$	58,075		$	74,992		$	119,153		$	137,238
Undistributed earnings allocated to restricted shares		(350	)		(435	)		(696	)		(806	)
Income available to Kirby common stockholders - basic		57,725			74,557			118,457			136,432
Undistributed earnings allocated to restricted shares		350			435			696			806
Undistributed earnings reallocated to restricted shares		(349	)		(434	)		(695	)		(803	)
Income available to Kirby common stockholders - diluted	$	57,726		$	74,558		$	118,458		$	136,435

Shares outstanding:
Weighted average common stock issued and outstanding		55,651			57,010			55,772			56,957
Weighted average unvested restricted stock		(336	)		(331	)		(326	)		(334	)
Weighted average common stock outstanding - basic		55,315			56,679			55,446			56,623
Dilutive effect of stock options		117			190			119			203
Weighted average common stock outstanding - diluted		55,432			56,869			55,565			56,826

Net earnings per share attributable to Kirby common stockholders:
Basic	$	1.04		$	1.32		$	2.14		$	2.41
Diluted	$	1.04		$	1.31		$	2.13		$	2.40

Certain outstanding options to purchase approximately 185,000 and 117,000 shares of common stock were excluded in the computation of diluted earnings per share as of June 30, 2015 and 2014, respectively, as such stock options would have been antidilutive.

RETIREMENT PLANS

6 Months Ended

Jun. 30, 2015

RETIREMENT PLANS [Abstract]

RETIREMENT PLANS

(10) RETIREMENT PLANS

The Company sponsors a defined benefit plan for its inland vessel personnel and shore based tankermen. The plan benefits are based on an employee’s years of service and compensation. The plan assets consist primarily of equity and fixed income securities.

The Company’s pension plan funding strategy has historically been to contribute an amount equal to the greater of the minimum required contribution under ERISA or the amount necessary to fully fund the plan on an accumulated benefit obligation (“ABO”) basis at the end of the fiscal year. The ABO is based on a variety of demographic and economic assumptions, and the pension plan assets’ returns are subject to various risks, including market and interest rate risk, making an accurate prediction of the pension plan contribution difficult. Based on current pension plan assets and market conditions, the Company expects to make a contribution of up to $5,000,000 to its pension plan prior to December 31, 2015 to fund its 2015 pension plan obligations. As of June 30, 2015, no 2015 year contributions have been made.

The Company sponsors an unfunded defined benefit health care plan that provides limited postretirement medical benefits to employees who meet minimum age and service requirements, and to eligible dependents. The plan limits cost increases in the Company’s contribution to 4% per year. The plan is contributory, with retiree contributions adjusted annually. The plan eliminated coverage for future retirees as of December 31, 2011. The Company also has an unfunded defined benefit supplemental executive retirement plan (“SERP”) that was assumed in an acquisition in 1999. That plan ceased to accrue additional benefits effective January 1, 2000.

The components of net periodic benefit cost for the Company’s defined benefit plans for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Pension Benefits
	Pension Plan								SERP
	Three months ended June 30,								Three months ended June 30,
	2015				2014				2015			2014
Components of net periodic benefit cost:
Service cost		$	3,517			$	2,556			$	—		$	—
Interest cost			3,302				3,198				16			19
Expected return on plan assets			(4,485	)			(4,718	)			—			—
Amortization of actuarial loss			1,903				155				7			4
Net periodic benefit cost		$	4,237			$	1,191			$	23		$	23

	Pension Benefits
	Pension Plan								SERP
	Six months ended June 30,								Six months ended June 30,
	2015				2014				2015			2014
Components of net periodic benefit cost:
Service cost		$	7,347			$	5,323			$	—		$	—
Interest cost			6,656				6,421				32			37
Expected return on plan assets			(8,968	)			(9,431	)			—			—
Amortization of actuarial loss			3,867				351				14			8
Net periodic benefit cost		$	8,902			$	2,664			$	46		$	45

The components of net periodic benefit cost for the Company’s postretirement benefit plan for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Other Postretirement Benefits								Other Postretirement Benefits
	Postretirement Welfare Plan								Postretirement Welfare Plan
	Three months ended June 30,								Six months ended June 30,
	2015				2014				2015				2014
Components of net periodic benefit cost:
Service cost		$	—			$	—			$	—			$	—
Interest cost			5				27				18				55
Amortization of actuarial gain			(222	)			(161	)			(395	)			(324	)
Net periodic benefit cost		$	(217	)		$	(134	)		$	(377	)		$	(269	)

CONTINGENCIES

6 Months Ended

Jun. 30, 2015

CONTINGENCIES [Abstract]

CONTINGENCIES

(11)	CONTINGENCIES

On March 22, 2014, a tank barge and towboat (the M/V Miss Susan), both owned by Kirby Inland Marine, LP, a wholly owned subsidiary of the Company, were involved in a collision with the M/S Summer Wind on the Houston Ship Channel near Texas City, Texas. The tank barge was damaged in the collision resulting in a discharge of intermediate fuel oil from one of its cargo tanks. The United States Coast Guard and the National Transportation Safety Board have named the Company and the Captain of the M/V Miss Susan, as well as the owner and the pilot of the M/S Summer Wind, as parties of interest in their investigation as to the cause of the incident. Sea Galaxy Ltd is the owner of the M/S Summer Wind. The Company is participating in the natural resource damage assessment and restoration process with federal and state government natural resource trustees.

The Company and the owner of the M/S Summer Wind have filed actions in the U.S. District Court for the Southern District of Texas seeking exoneration from or limitation of liability relating to the foregoing incident as provided for in the federal rules of procedure for maritime claims. The two actions have been consolidated for procedural purposes since they both arise out of the same occurrence. There is a separate process for making a claim under the Oil Pollution Act of 1990 (“OPA”). The Company is processing claims properly presented, documented and recoverable under OPA. The Company is named as a party in other lawsuits filed in connection with this incident which are currently stayed by orders entered into by the court in the limitation proceedings, some of which may also have been presented as claims in the limitation proceeding. The actions include allegation of business interruption, loss of profit, loss of use of natural resources and seek unspecified economic and compensatory damages. In addition, the Company has received claims from numerous parties claiming property damage and various economic damages. The Company has also been named as a defendant in a civil action by two crewmembers of the M/V Miss Susan, alleging damages under the general maritime law and the Jones Act. The litigation and claims process is ongoing. The Company believes it has adequate insurance coverage for pollution, marine and other potential liabilities arising from the incident. The Company believes it has accrued adequate reserves for the incident and does not expect the incident to have a material adverse effect on its business or financial condition.

In June 2011, the Company as well as three other companies received correspondence from the United States Environmental Protection Agency (“EPA”) concerning ongoing cleanup and restoration activities under the Comprehensive Environmental Response, Compensation and Liability Act (“CERCLA”) with respect to a Superfund site, the Gulfco Marine Maintenance Site (“Gulfco”), located in Freeport, Texas. In prior years, various subsidiaries of the Company utilized a successor to Gulfco to perform tank barge cleaning services, sand blasting and repair on certain Company vessels. Since 2005, four named Potentially Responsible Parties (“PRPs”) have participated in the investigation, cleanup and restoration of the site under an administrative order from EPA. Information received to date indicates that approximately $9,943,000 was incurred in connection with the cleanup effort in addition to EPA’s oversight costs of approximately $2,258,000. The named PRPs filed suit against the Company and approximately 21 other defendants seeking contribution and indemnity under CERCLA for costs incurred in connection with its activities in cleaning up the Gulfco Site. The Company has filed responsive pleadings in this matter and believes it has accrued an adequate reserve based on the information provided by the plaintiffs to date. The EPA has issued notice letters under Section 107(a) of CERCLA to the Company and other nonparticipating PRPs to initiate settlement negotiations of EPA’s claim for its past costs for the Site. The Company and other nonparticipating PRPs continue to discuss resolution of this matter with EPA and the Gulfco Restoration Group.

The Company is also involved in various legal and other proceedings which are incidental to the conduct of its business, none of which in the opinion of management will have a material effect on the Company’s financial condition, results of operations or cash flows. Management believes that it has recorded adequate reserves and believes that it has adequate insurance coverage or has meritorious defenses for these other claims and contingencies.

The Company has issued guaranties or obtained standby letters of credit and performance bonds supporting performance by the Company and its subsidiaries of contractual or contingent legal obligations of the Company and its subsidiaries incurred in the ordinary course of business. The aggregate notional value of these instruments is $28,489,000 at June 30, 2015, including $8,125,000 in letters of credit and $20,364,000 in performance bonds. All of these instruments have an expiration date within four years. The Company does not believe demand for payment under these instruments is likely and expects no material cash outlays to occur in connection with these instruments.

STOCK AWARD PLANS (Tables)

6 Months Ended

Jun. 30, 2015

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Compensation cost breakdown in statement of earnings

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
Compensation cost		$	2,713		$	3,120		$	5,251		$	5,273
Income tax benefit		$	1,015		$	1,182		$	1,964		$	1,998

Summary of Stock option valuation assumptions

The key input variables used in valuing the options during the six months ended June 30, 2015 and 2014 were as follows:

	Six months ended June 30,
	2015		2014
Dividend yield	None		None
Average risk-free interest rate		1.3%		2.0%
Stock price volatility		33%		33%
Estimated option term	Six years		Six or seven years

Employee Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of stock option activity

The following is a summary of the stock option activity under the employee plan described above for the six months ended June 30, 2015:

	Outstanding Non- Qualified or Nonincentive Stock Awards			Weighted Average Exercise Price
Outstanding at December 31, 2014		322,956		$	69.95
Granted		114,894		$	74.99
Exercised		─			─
Forfeited		(7,418	)	$	86.28
Outstanding at June 30, 2015		430,432		$	71.01

Summary of outstanding and exercisable stock options

The following table summarizes information about the Company’s outstanding and exercisable stock options under the employee plan at June 30, 2015:

		Options Outstanding							Options Exercisable
Range of Exercise Prices		Number Outstanding		Weighted Average Remaining Contractual Life in Years		Weighted Average Exercise Price		Aggregate Intrinsic Value	Number Exercisable		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	31.35 - $ 36.35		16,910		1.6	$	32.82			16,910	$	32.82
$	46.74		56,629		2.6	$	46.74			56,629	$	46.74
$	65.28 - $ 74.99		283,963		5.1	$	70.98			141,669	$	67.90
$	93.64 - $ 96.85		35,763		5.6	$	94.27			11,921	$	94.27
$	101.46 -$114.11		37,167		5.7	$	103.22			12,389	$	103.22
$	31.35 -$114.11		430,432		4.7	$	71.01	$4,047,000		239,518	$	63.56	$3,677,000

Summary of restricted stock award activity

The following is a summary of the restricted stock award activity under the employee plan described above for the six months ended June 30, 2015:

	Unvested Restricted Stock Award Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested balance at December 31, 2014		321,453		$	71.04
Granted		122,740		$	75.04
Vested		(113,470	)	$	60.75
Forfeited		(10,617	)	$	85.45
Nonvested balance at June 30, 2015		320,106		$	75.74

Director Plan [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of stock option activity

The following is a summary of the stock option activity under the director plan described above for the six months ended June 30, 2015:

	Outstanding Non- Qualified or Nonincentive Stock Options			Weighted Average Exercise Price
Outstanding at December 31, 2014	298,334		$	60.01
Granted	─		$	─
Exercised	(77,905	)	$	47.65
Outstanding at June 30, 2015	220,429		$	64.37

Summary of outstanding and exercisable stock options

The following table summarizes information about the Company’s outstanding and exercisable stock options under the director plan at June 30, 2015:

		Options Outstanding							Options Exercisable
Range of Exercise Prices		Number Outstanding		Weighted Average Remaining Contractual Life in Years		Weighted Average Exercise Price		Aggregate Intrinsic Value	Number Exercisable		Weighted Average Exercise Price		Aggregate Intrinsic Value
$	29.60 - $36.82		30,000		2.4	$	33.60			30,000	$	33.60
$	41.24 - $56.45		71,276		4.8	$	52.34			71,276	$	52.34
$	61.89 - $62.48		41,153		7.0	$	62.34			41,153	$	62.34
$	75.17 - $99.52		78,000		7.8	$	88.28			78,000	$	88.28
$	29.60 - $99.52		220,429		5.9	$	64.37	$3,668,000		220,429	$	64.37	$3,668,000

Summary of restricted stock award activity

The following is a summary of the restricted stock award activity under the director plan described above for the six months ended June 30, 2015:

	Unvested Restricted Stock Award Shares			Weighted Average Grant Date Fair Value Per Share
Nonvested balance at December 31, 2014		292		$	99.52
Granted		18,843		$	79.46
Vested		(575	)	$	89.65
Nonvested balance at June 30, 2015		18,560		$	79.46

OTHER COMPREHENSIVE INCOME (Tables)

6 Months Ended

Jun. 30, 2015

OTHER COMPREHENSIVE INCOME [Abstract]

Schedule of changes in other comprehensive income

The Company’s changes in other comprehensive income for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Three months ended June 30,
	2015										2014
	Gross Amount			Income Tax (Provision) Benefit				Net Amount			Gross Amount				Income Tax (Provision) Benefit				Net Amount

Pension and postretirement benefits (a):
Amortization of net actuarial loss		$	1,688		$	(642	)		$	1,046		$	(2	)		$	—			$	(2	)
Actuarial gains			2,293			(881	)			1,412			721				(275	)			446
Foreign currency translation adjustments			129			—				129			9				—				9
Change in fair value of derivative instruments (b):
Reclassified to net earnings			—			—				—			—				—				—
Total		$	4,110		$	(1,523	)		$	2,587		$	728			$	(275	)		$	453

	Six months ended June 30,
	2015										2014
	Gross Amount			Income Tax (Provision) Benefit				Net Amount			Gross Amount				Income Tax (Provision) Benefit				Net Amount

Pension and postretirement benefits (a):
Amortization of net actuarial loss		$	3,486		$	(1,332	)		$	2,154		$	35			$	(13	)		$	22
Actuarial gains			2,293			(881	)			1,412			721				(275	)			446
Foreign currency translation adjustments			32			—				32			(8	)			—				(8	)
Change in fair value of derivative instruments (b):
Reclassified to net earnings			—			—				—			146				(62	)			84
Total		$	5,811		$	(2,213	)		$	3,598		$	894			$	(350	)		$	544

(a)

Actuarial gains (losses) are amortized into costs of sales and operating expenses or selling, general and administrative expenses as appropriate. (See Note 10 – Retirement Plans)

(b)

Reclassifications to net earnings of derivatives qualifying as effective hedges are recognized in costs of sales and operating expenses.

SEGMENT DATA (Tables)

6 Months Ended

Jun. 30, 2015

SEGMENT DATA [Abstract]

Schedule of segment reporting information, by segment

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014
Revenues:
Marine transportation	$	425,053		$	456,745		$	844,958		$	892,516
Diesel engine services		118,103			171,309			285,871			324,784
	$	543,156		$	628,054		$	1,130,829		$	1,217,300
Segment profit (loss):
Marine transportation	$	97,011		$	115,968		$	193,280		$	213,519
Diesel engine services		4,931			14,337			13,774			27,109
Other		(8,870	)		(8,626	)		(16,080	)		(17,949	)
	$	93,072		$	121,679		$	190,974		$	222,679

	June 30, 2015		December 31, 2014
Total assets:
Marine transportation	$	3,425,973	$	3,317,696
Diesel engine services		673,675		736,129
Other		54,855		88,084
	$	4,154,503	$	4,141,909

Schedule of other segment reporting information

The following table presents the details of “Other” segment loss for the three months and six months ended June 30, 2015 and 2014 (in thousands):

	Three months ended June 30,								Six months ended June 30,
	2015				2014				2015				2014

General corporate expenses		$	(3,899	)		$	(3,807	)		$	(7,474	)		$	(7,327	)
Gain on disposition of assets			91				527				1,646				578
Interest expense			(4,759	)			(5,469	)			(10,009	)			(11,087	)
Other income (expense)			(303	)			123				(243	)			(113	)
		$	(8,870	)		$	(8,626	)		$	(16,080	)		$	(17,949	)

The following table presents the details of “Other” total assets as of June 30, 2015 and December 31, 2014 (in thousands):

	June 30, 2015		December 31, 2014
General corporate assets	$	52,983	$	85,545
Investment in affiliates		1,872		2,539
	$	54,855	$	88,084

EARNINGS PER SHARE (Tables)

6 Months Ended

Jun. 30, 2015

EARNINGS PER SHARE [Abstract]

Components of basic and diluted earnings per share

	Three months ended June 30,						Six months ended June 30,
	2015			2014			2015			2014

Net earnings attributable to Kirby	$	58,075		$	74,992		$	119,153		$	137,238
Undistributed earnings allocated to restricted shares		(350	)		(435	)		(696	)		(806	)
Income available to Kirby common stockholders - basic		57,725			74,557			118,457			136,432
Undistributed earnings allocated to restricted shares		350			435			696			806
Undistributed earnings reallocated to restricted shares		(349	)		(434	)		(695	)		(803	)
Income available to Kirby common stockholders - diluted	$	57,726		$	74,558		$	118,458		$	136,435

Shares outstanding:
Weighted average common stock issued and outstanding		55,651			57,010			55,772			56,957
Weighted average unvested restricted stock		(336	)		(331	)		(326	)		(334	)
Weighted average common stock outstanding - basic		55,315			56,679			55,446			56,623
Dilutive effect of stock options		117			190			119			203
Weighted average common stock outstanding - diluted		55,432			56,869			55,565			56,826

Net earnings per share attributable to Kirby common stockholders:
Basic	$	1.04		$	1.32		$	2.14		$	2.41
Diluted	$	1.04		$	1.31		$	2.13		$	2.40

RETIREMENT PLANS (Tables)

6 Months Ended

Jun. 30, 2015

Pension Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

Components of Net Periodic Benefit Cost

The components of net periodic benefit cost for the Company’s defined benefit plans for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Pension Benefits
	Pension Plan								SERP
	Three months ended June 30,								Three months ended June 30,
	2015				2014				2015			2014
Components of net periodic benefit cost:
Service cost		$	3,517			$	2,556			$	—		$	—
Interest cost			3,302				3,198				16			19
Expected return on plan assets			(4,485	)			(4,718	)			—			—
Amortization of actuarial loss			1,903				155				7			4
Net periodic benefit cost		$	4,237			$	1,191			$	23		$	23

	Pension Benefits
	Pension Plan								SERP
	Six months ended June 30,								Six months ended June 30,
	2015				2014				2015			2014
Components of net periodic benefit cost:
Service cost		$	7,347			$	5,323			$	—		$	—
Interest cost			6,656				6,421				32			37
Expected return on plan assets			(8,968	)			(9,431	)			—			—
Amortization of actuarial loss			3,867				351				14			8
Net periodic benefit cost		$	8,902			$	2,664			$	46		$	45

Other Postretirement Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

Components of Net Periodic Benefit Cost

The components of net periodic benefit cost for the Company’s postretirement benefit plan for the three months and six months ended June 30, 2015 and 2014 were as follows (in thousands):

	Other Postretirement Benefits								Other Postretirement Benefits
	Postretirement Welfare Plan								Postretirement Welfare Plan
	Three months ended June 30,								Six months ended June 30,
	2015				2014				2015				2014
Components of net periodic benefit cost:
Service cost		$	—			$	—			$	—			$	—
Interest cost			5				27				18				55
Amortization of actuarial gain			(222	)			(161	)			(395	)			(324	)
Net periodic benefit cost		$	(217	)		$	(134	)		$	(377	)		$	(269	)

STOCK AWARD PLANS (Details) (USD $)	3 Months Ended		6 Months Ended
STOCK AWARD PLANS (Details) (USD $)	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
STOCK AWARD PLANS [Abstract]
Compensation cost	$ 2,713,000	$ 3,120,000	$ 5,251,000	$ 5,273,000
Income tax benefit	1,015,000	1,182,000	1,964,000	1,998,000
Share based Compensation Plans Combined Disclosure [Abstract]
Intrinsic value of stock options exercised			2,555,000	11,456,000
Tax benefit from stock options exercised			956,000	4,342,000
Intrinsic value of restricted stock vesting			9,015,000	13,949,000
Tax benefit from restricted stock vesting			3,372,000	5,287,000
Fair value of options vested			2,194,000	2,076,000
Fair value of restricted stock vested			9,015,000	13,949,000
Fair value of stock options granted (in dollars per share)			$ 25.18	$ 36.05
Fair value of stock options granted			2,893,000	4,226,000
Fair Value Assumptions [Abstract]
Dividend yield (in hundredths)			0.00%	0.00%
Average risk-free interest rate (in hundredths)			1.30%	2.00%
Stock price volatility (in hundredths)			33.00%	33.00%
Estimated option term			6 years
Minimum [Member]
Fair Value Assumptions [Abstract]
Estimated option term				6 years
Maximum [Member]
Fair Value Assumptions [Abstract]
Estimated option term				7 years
Employee Stock Award Plan [Member]
Stock Award Plan Information [Abstract]
Term of grant			7 years
Vesting period			3 years
Shares available for future grants (in shares)	2,321,347		2,321,347
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			322,956
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			114,894
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			0
Forfeited, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			(7,418)
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)	430,432		430,432
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share)			$ 69.95
Granted, Weighted Average Exercise Price (in dollars per share)			$ 74.99
Exercised, Weighted Average Exercise Price (in dollars per share)			$ 0
Forfeited, Weighted Average Exercise Price (in dollars per share)			$ 86.28
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share)	$ 71.01		$ 71.01
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares (in shares)			321,453
Granted, Unvested Restricted Stock Award Shares (in shares)			122,740
Vested, Unvested Restricted Stock Award Shares (in shares)			(113,470)
Forfeited, Unvested Restricted Stock Award Shares (in shares)			(10,617)
Nonvested balance end of period, Unvested Restricted Stock Award Shares (in shares)	320,106		320,106
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 71.04
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 75.04
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 60.75
Forfeited, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 85.45
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 75.74		$ 75.74
Employee Stock Award Plan [Member] \| First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 36.35
Range of Exercise Prices, lower limit (in dollars per share)			$ 31.35
Options Outstanding [Abstract]
Number Outstanding (in shares)	16,910		16,910
Weighted Average Remaining Contractual Life (in years)			1 year 7 months 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 32.82		$ 32.82
Options Exercisable [Abstract]
Number Exercisable (in shares)	16,910		16,910
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 32.82		$ 32.82
Employee Stock Award Plan [Member] \| Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, lower limit (in dollars per share)			$ 46.74
Options Outstanding [Abstract]
Number Outstanding (in shares)	56,629		56,629
Weighted Average Remaining Contractual Life (in years)			2 years 7 months 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 46.74		$ 46.74
Options Exercisable [Abstract]
Number Exercisable (in shares)	56,629		56,629
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 46.74		$ 46.74
Employee Stock Award Plan [Member] \| Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 74.99
Range of Exercise Prices, lower limit (in dollars per share)			$ 65.28
Options Outstanding [Abstract]
Number Outstanding (in shares)	283,963		283,963
Weighted Average Remaining Contractual Life (in years)			5 years 1 month 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 70.98		$ 70.98
Options Exercisable [Abstract]
Number Exercisable (in shares)	141,669		141,669
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 67.90		$ 67.90
Employee Stock Award Plan [Member] \| Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 96.85
Range of Exercise Prices, lower limit (in dollars per share)			$ 93.64
Options Outstanding [Abstract]
Number Outstanding (in shares)	35,763		35,763
Weighted Average Remaining Contractual Life (in years)			5 years 7 months 6 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 94.27		$ 94.27
Options Exercisable [Abstract]
Number Exercisable (in shares)	11,921		11,921
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 94.27		$ 94.27
Employee Stock Award Plan [Member] \| Fifth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 114.11
Range of Exercise Prices, lower limit (in dollars per share)			$ 101.46
Options Outstanding [Abstract]
Number Outstanding (in shares)	37,167		37,167
Weighted Average Remaining Contractual Life (in years)			5 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 103.22		$ 103.22
Options Exercisable [Abstract]
Number Exercisable (in shares)	12,389		12,389
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 103.22		$ 103.22
Employee Stock Award Plan [Member] \| Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 114.11
Range of Exercise Prices, lower limit (in dollars per share)			$ 31.35
Options Outstanding [Abstract]
Number Outstanding (in shares)	430,432		430,432
Weighted Average Remaining Contractual Life (in years)			4 years 8 months 12 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 71.01		$ 71.01
Aggregate Intrinsic Value, Options Outstanding	4,047,000		4,047,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	239,518		239,518
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 63.56		$ 63.56
Aggregate Intrinsic Value, Options Exercisable	3,677,000		3,677,000
2000 Director Plan [Member]
Stock Award Plan Information [Abstract]
Term of grant			10 years
Vesting period			6 months
Shares available for future grants (in shares)	541,038		541,038
Outstanding Non-Qualified or Nonincentive Stock Awards [Roll Forward]
Outstanding at Period Start, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			298,334
Granted, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			0
Exercised, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)			(77,905)
Outstanding at Period End, Outstanding Non-Qualified or Nonincentive Stock Awards (in shares)	220,429		220,429
Weighted Average Exercise Price [Abstract]
Outstanding at Period Start, Weighted Average Exercise Price (in dollars per share)			$ 60.01
Granted, Weighted Average Exercise Price (in dollars per share)			$ 0
Exercised, Weighted Average Exercise Price (in dollars per share)			$ 47.65
Outstanding at Period End, Weighted Average Exercise Price (in dollars per share)	$ 64.37		$ 64.37
Unvested Restricted Stock Award Shares [Roll Forward]
Nonvested balance beginning of period, Unvested Restricted Stock Award Shares (in shares)			292
Granted, Unvested Restricted Stock Award Shares (in shares)			18,843
Vested, Unvested Restricted Stock Award Shares (in shares)			(575)
Nonvested balance end of period, Unvested Restricted Stock Award Shares (in shares)	18,560		18,560
Weighted Average Grant Date Fair Value Per Share [Abstract]
Nonvested balance beginning of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 99.52
Granted, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 79.46
Vested, Weighted Average Grant Date Fair Value Per Share (in dollars per share)			$ 89.65
Nonvested balance end of period, Weighted Average Grant Date Fair Value Per Share (in dollars per share)	$ 79.46		$ 79.46
2000 Director Plan [Member] \| First Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 36.82
Range of Exercise Prices, lower limit (in dollars per share)			$ 29.60
Options Outstanding [Abstract]
Number Outstanding (in shares)	30,000		30,000
Weighted Average Remaining Contractual Life (in years)			2 years 4 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 33.60		$ 33.60
Options Exercisable [Abstract]
Number Exercisable (in shares)	30,000		30,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 33.60		$ 33.60
2000 Director Plan [Member] \| Second Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 56.45
Range of Exercise Prices, lower limit (in dollars per share)			$ 41.24
Options Outstanding [Abstract]
Number Outstanding (in shares)	71,276		71,276
Weighted Average Remaining Contractual Life (in years)			4 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 52.34		$ 52.34
Options Exercisable [Abstract]
Number Exercisable (in shares)	71,276		71,276
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 52.34		$ 52.34
2000 Director Plan [Member] \| Third Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 62.48
Range of Exercise Prices, lower limit (in dollars per share)			$ 61.89
Options Outstanding [Abstract]
Number Outstanding (in shares)	41,153		41,153
Weighted Average Remaining Contractual Life (in years)			7 years
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 62.34		$ 62.34
Options Exercisable [Abstract]
Number Exercisable (in shares)	41,153		41,153
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 62.34		$ 62.34
2000 Director Plan [Member] \| Fourth Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 99.52
Range of Exercise Prices, lower limit (in dollars per share)			$ 75.17
Options Outstanding [Abstract]
Number Outstanding (in shares)	78,000		78,000
Weighted Average Remaining Contractual Life (in years)			7 years 9 months 18 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 88.28		$ 88.28
Options Exercisable [Abstract]
Number Exercisable (in shares)	78,000		78,000
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 88.28		$ 88.28
2000 Director Plan [Member] \| Full Exercise Price Range [Member]
Outstanding and Exercisable Stock options [Abstract]
Range of Exercise Prices, upper limit (in dollars per share)			$ 99.52
Range of Exercise Prices, lower limit (in dollars per share)			$ 29.60
Options Outstanding [Abstract]
Number Outstanding (in shares)	220,429		220,429
Weighted Average Remaining Contractual Life (in years)			5 years 10 months 24 days
Weighted Average Exercise Price, Options Outstanding (in dollars per share)	$ 64.37		$ 64.37
Aggregate Intrinsic Value, Options Outstanding	3,668,000		3,668,000
Options Exercisable [Abstract]
Number Exercisable (in shares)	220,429		220,429
Weighted Average Exercise Price, Options Exercisable (in dollars per share)	$ 64.37		$ 64.37
Aggregate Intrinsic Value, Options Exercisable	3,668,000		3,668,000
Stock Options [Member]
Share based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	4,204,000		4,204,000
Weighted average period of recognition in years			1 year 8 months 12 days
Restricted Stock [Member]
Share based Compensation Plans Combined Disclosure [Abstract]
Unrecognized compensation cost related to unvested awards	$ 22,036,000		$ 22,036,000
Weighted average period of recognition in years			3 years 2 months 12 days

OTHER COMPREHENSIVE INCOME (Details) (USD $)
In Thousands, unless otherwise specified

3 Months Ended

6 Months Ended

Jun. 30, 2015

Jun. 30, 2014

Jun. 30, 2015

Jun. 30, 2014

Pension and postretirement benefits [Abstract]

Amortization of net actuarial loss, Gross Amount

$ 1,688

^[1]

$ (2)

^[1]

$ 3,486

^[1]

$ 35

^[1]

Amortization of net actuarial loss, Income Tax (Provision) Benefit

(642)

^[1]

(1,332)

^[1]

(13)

^[1]

Amortization of net actuarial loss, Net Amount

1,046

^[1]

(2)

^[1]

2,154

^[1]

Actuarial gains, Gross Amount

2,293

^[1]

721

^[1]

2,293

^[1]

721

^[1]

Actuarial gains, Income Tax (Provision) Benefit

(881)

^[1]

(275)

^[1]

(881)

^[1]

(275)

^[1]

Actuarial gains, Net Amount

1,412

^[1]

446

^[1]

1,412

^[1]

446

^[1]

Foreign currency translation adjustments, Gross Amount

129

^[1]

(8)

^[1]

Foreign currency translation adjustments, Income Tax (Provision) Benefit

^[1]

Foreign currency translation adjustments, Net Amount

129

(8)

Change in fair value of derivative instruments [Abstract]

Reclassified to net earnings, Gross Amount

^[2]

146

^[2]

Reclassified to net earnings, Income Tax (Provision) Benefit

^[2]

(62)

^[2]

Reclassified to net earnings, Net Amount

^[2]

Total other comprehensive income (loss), Gross Amount

4,110

728

5,811

^[2]

894

^[2]

Total other comprehensive income (loss), Income Tax (Provision) Benefit

(1,523)

(275)

(2,213)

^[2]

(350)

^[2]

Total comprehensive income, net of taxes

$ 2,587

$ 453

$ 3,598

$ 544

[1]	Actuarial gains (losses) are amortized into costs of sales and operating expenses or selling, general and administrative expenses as appropriate. (See Note 10 - Retirement Plans)
[2]	Reclassifications to net earnings of derivatives qualifying as effective hedges are recognized in costs of sales and operating expenses.

SEGMENT DATA (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015 Segment	Jun. 30, 2014	Dec. 31, 2014
SEGMENT DATA [Abstract]
Number of reportable segments			2
Revenues [Abstract]
Marine transportation	$ 425,053	$ 456,745	$ 844,958	$ 892,516
Diesel engine services	118,103	171,309	285,871	324,784
Total revenues	543,156	628,054	1,130,829	1,217,300
Segment profit (loss)	93,072	121,679	190,974	222,679
Total assets	4,154,503		4,154,503		4,141,909
Other segment disclosures [Abstract]
Gain on disposition of assets	91	527	1,646	578
Interest expense	(4,759)	(5,469)	(10,009)	(11,087)
Other income (expense)	(303)	123	(243)	(113)
Other [Member]
Revenues [Abstract]
Segment profit (loss)	(8,870)	(8,626)	(16,080)	(17,949)
Total assets	54,855		54,855		88,084
Other segment disclosures [Abstract]
General corporate expenses	(3,899)	(3,807)	(7,474)	(7,327)
Gain on disposition of assets	91	527	1,646	578
Interest expense	(4,759)	(5,469)	(10,009)	(11,087)
Other income (expense)	(303)	123	(243)	(113)
Profit (loss) from other segment	(8,870)	(8,626)	(16,080)	(17,949)
Details of "Other" total assets [Abstract]
General corporate assets	52,983		52,983		85,545
Investment in affiliates	1,872		1,872		2,539
Total other assets	54,855		54,855		88,084
Reporting Segments [Member] \| Marine transportation [Member]
Revenues [Abstract]
Marine transportation	425,053	456,745	844,958	892,516
Segment profit (loss)	97,011	115,968	193,280	213,519
Total assets	3,425,973		3,425,973		3,317,696
Reporting Segments [Member] \| Diesel engine services [Member]
Revenues [Abstract]
Diesel engine services	118,103	171,309	285,871	324,784
Segment profit (loss)	4,931	14,337	13,774	27,109
Total assets	$ 673,675		$ 673,675		$ 736,129

TAXES ON INCOME (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
TAXES ON INCOME [Abstract]
Earnings before taxes on income - United States	$ 93,072	$ 121,679	$ 190,974	$ 222,679
Federal [Abstract]
Current	25,086	35,671	51,266	61,167
Deferred	6,919	5,629	14,401	14,413
State and local	2,691	4,468	5,520	8,177
Total Provision for taxes on income	$ 34,696	$ 45,768	$ 71,187	$ 83,757

EARNINGS PER SHARE (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
EARNINGS PER SHARE [Abstract]
Net earnings attributable to Kirby	$ 58,075	$ 74,992	$ 119,153	$ 137,238
Undistributed earnings allocated to restricted shares	(350)	(435)	(696)	(806)
Income available to Kirby common stockholders - basic	57,725	74,557	118,457	136,432
Undistributed earnings allocated to restricted shares	350	435	696	806
Undistributed earnings reallocated to restricted shares	(349)	(434)	(695)	(803)
Income available to Kirby common stockholders - diluted	$ 57,726	$ 74,558	$ 118,458	$ 136,435
Shares Outstanding: [Abstract]
Weighted average common stock issued and outstanding (in shares)	55,651,000	57,010,000	55,772,000	56,957,000
Weighted average unvested restricted stock (in shares)	(336,000)	(331,000)	(326,000)	(334,000)
Weighted average common stock outstanding - basic (in shares)	55,315,000	56,679,000	55,446,000	56,623,000
Dilutive effect of stock options (in shares)	117,000	190,000	119,000	203,000
Weighted average common stock outstanding - diluted (in shares)	55,432,000	56,869,000	55,565,000	56,826,000
Net earnings per share attributable to Kirby common stockholders:
Basic (in dollars per share)	$ 1.04	$ 1.32	$ 2.14	$ 2.41
Diluted (in dollars per share)	$ 1.04	$ 1.31	$ 2.13	$ 2.40
Antidilutive Securities Excluded from Computation of Earnings Per Share (in shares)			185,000	117,000

RETIREMENT PLANS (Details) (USD $)	3 Months Ended		6 Months Ended
RETIREMENT PLANS (Details) (USD $)	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Pension Plan [Member]
Components of net periodic benefit cost: [Abstract]
Service cost	$ 3,517,000	$ 2,556,000	$ 7,347,000	$ 5,323,000
Interest cost	3,302,000	3,198,000	6,656,000	6,421,000
Expected return on plan assets	(4,485,000)	(4,718,000)	(8,968,000)	(9,431,000)
Amortization of actuarial loss	1,903,000	155,000	3,867,000	351,000
Net periodic benefit cost	4,237,000	1,191,000	8,902,000	2,664,000
Pension Plan [Member] \| Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan of asset contributions to pension plan obligations	5,000,000		5,000,000
SERP [Member]
Components of net periodic benefit cost: [Abstract]
Service cost	0	0	0	0
Interest cost	16,000	19,000	32,000	37,000
Expected return on plan assets	0	0	0	0
Amortization of actuarial loss	7,000	4,000	14,000	8,000
Net periodic benefit cost	23,000	23,000	46,000	45,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension plan defined benefit plan cost increase limit percentage (in hundredths)			4.00%
Components of net periodic benefit cost: [Abstract]
Service cost	0	0	0	0
Interest cost	5,000	27,000	18,000	55,000
Amortization of actuarial loss	(222,000)	(161,000)	(395,000)	(324,000)
Net periodic benefit cost	$ (217,000)	$ (134,000)	$ (377,000)	$ (269,000)

CONTINGENCIES (Details) (USD $)	6 Months Ended
CONTINGENCIES (Details) (USD $)	Jun. 30, 2015
Guarantor Obligations [Line Items]
Issued guaranties	$ 28,489,000
Maximum [Member]
Guarantor Obligations [Line Items]
Guarantor obligations, expiration period	4 years
Performance Bonds [Member]
Guarantor Obligations [Line Items]
Issued guaranties	20,364,000
Standby Letters Of Credit [Member]
Guarantor Obligations [Line Items]
Issued guaranties	8,125,000
Gulfco Marine Superfund Site [Member]
Guarantor Obligations [Line Items]
Number of other companies also named as Potentially Responsible Parties ("PRPs")	3
Number of companies named as Potentially Responsible Parties ("PRPs")	4
EPA incurred cleanup expense	9,943,000
EPA oversight costs	$ 2,258,000
Number of defendants seeking contribution and indemnity under CERCLA	21
Collision with M/S Summer Wind [Member]
Loss Contingencies [Line Items]
Number of vessels damaged in collision resulting in fuel oil discharge	1
Number of actions filed against the Company	2
Number of crewmembers alleging damages	2

FAIR VALUE MEASUREMENTS	6 Months Ended
FAIR VALUE MEASUREMENTS	Jun. 30, 2015
FAIR VALUE MEASUREMENTS [Abstract]
FAIR VALUE MEASUREMENTS	(4) FAIR VALUE MEASUREMENTS The estimated fair value of total debt outstanding at June 30, 2015 and December 31, 2014 was $796,913,000 and $705,215,000, respectively, which differs from the carrying amounts of $808,300,000 and $716,700,000, respectively, included in the consolidated financial statements. The fair value was determined using an income approach that relies on inputs such as yield curves. Cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities have carrying values that approximate fair value due to the short-term maturity of these financial instruments. Certain assets are measured at fair value on a nonrecurring basis. These assets are adjusted to fair value when there is evidence of impairment. During the six months ended June 30, 2015, there was no indication that the Company’s long-lived assets were impaired, and accordingly, measurement at fair value was not required.

INVENTORIES (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2015	Dec. 31, 2014
Details of inventories [Abstract]
Finished goods	$ 171,484	$ 179,760
Work in process	19,577	12,594
Inventory, Net, Total	$ 191,061	$ 192,354

FAIR VALUE MEASUREMENTS (Details) (USD $)	Jun. 30, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Estimated fair value of outstanding debt	$ 796,913,000	$ 705,215,000
Carrying amount of debt	$ 808,300,000	$ 716,700,000