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Overhaul and repair of medium-speed and high-speed diesel engines, reduction gear repair, and sale of related parts and accessories for customers in the marine, power generation and railroad industries.

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The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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Amount of gain (loss) on sale or disposal of property, plant and equipment assets, excluding oil and gas property and timber property.

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Amount of the cost of borrowed funds accounted for as interest expense.

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Segment Data (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014 Segment	Dec. 31, 2013	Dec. 31, 2012
Segment Data [Abstract]
Number of Reportable Segments									2us-gaap_NumberOfReportableSegments
Revenues [Abstract]
Marine transportation									$ 1,770,684us-gaap_CargoAndFreightRevenue	$ 1,713,167us-gaap_CargoAndFreightRevenue	$ 1,408,893us-gaap_CargoAndFreightRevenue
Diesel engine services									795,634	529,028	703,765
Total revenues	668,297us-gaap_Revenues	680,721us-gaap_Revenues	628,054us-gaap_Revenues	589,246us-gaap_Revenues	568,397us-gaap_Revenues	551,105us-gaap_Revenues	563,908us-gaap_Revenues	558,785us-gaap_Revenues	2,566,318us-gaap_Revenues	2,242,195us-gaap_Revenues	2,112,658us-gaap_Revenues
Segment profit (loss)	108,783	122,928	121,679	101,000	102,905	111,703	102,134	91,936	454,390	408,678	340,526
Total assets	4,141,909us-gaap_Assets				3,682,517us-gaap_Assets				4,141,909us-gaap_Assets	3,682,517us-gaap_Assets	3,653,128us-gaap_Assets
Depreciation and amortization									169,312	164,437	145,147
Capital expenditures									355,144	253,227	312,167
Other segment disclosures [Abstract]
Interest expense	(5,149)us-gaap_InterestExpense	(5,225)us-gaap_InterestExpense	(5,469)us-gaap_InterestExpense	(5,618)us-gaap_InterestExpense	(5,971)us-gaap_InterestExpense	(6,694)us-gaap_InterestExpense	(7,219)us-gaap_InterestExpense	(7,988)us-gaap_InterestExpense	(21,461)us-gaap_InterestExpense	(27,872)us-gaap_InterestExpense	(24,385)us-gaap_InterestExpense
Gain (loss) on disposition of assets	(156)us-gaap_GainLossOnDispositionOfAssets	(47)us-gaap_GainLossOnDispositionOfAssets	(527)us-gaap_GainLossOnDispositionOfAssets	(51)us-gaap_GainLossOnDispositionOfAssets	(160)us-gaap_GainLossOnDispositionOfAssets	(223)us-gaap_GainLossOnDispositionOfAssets	(537)us-gaap_GainLossOnDispositionOfAssets	32us-gaap_GainLossOnDispositionOfAssets	(781)us-gaap_GainLossOnDispositionOfAssets	(888)us-gaap_GainLossOnDispositionOfAssets	14us-gaap_GainLossOnDispositionOfAssets
Other income (expense)	125us-gaap_NonoperatingIncomeExpense	27us-gaap_NonoperatingIncomeExpense	123us-gaap_NonoperatingIncomeExpense	(236)us-gaap_NonoperatingIncomeExpense	132us-gaap_NonoperatingIncomeExpense	60us-gaap_NonoperatingIncomeExpense	101us-gaap_NonoperatingIncomeExpense	75us-gaap_NonoperatingIncomeExpense	(345)us-gaap_NonoperatingIncomeExpense	20us-gaap_NonoperatingIncomeExpense	(198)us-gaap_NonoperatingIncomeExpense
Details of "Other" total assets [Abstract]
Investment in affiliates	2,539				2,156				2,539	2,156
Total assets	4,141,909us-gaap_Assets				3,682,517us-gaap_Assets				4,141,909us-gaap_Assets	3,682,517us-gaap_Assets	3,653,128us-gaap_Assets
Reporting Segments [Member]
Revenues [Abstract]
Marine transportation									1,770,684	1,713,167	1,408,893
Diesel engine services									795,634	529,028	703,765
Total revenues									2,566,318	2,242,195	2,112,658
Segment profit (loss)									454,390	408,678	340,526
Depreciation and amortization									169,312	164,437	145,147
Capital expenditures									355,144	253,227	312,167
Marine Transportation [Member] \| Reporting Segments [Member]
Revenues [Abstract]
Segment profit (loss)									429,864	408,255	311,755
Total assets	3,317,696				3,046,692				3,317,696	3,046,692	2,951,723
Depreciation and amortization									154,019	149,574	129,857
Capital expenditures									340,315	237,964	274,351
Details of "Other" total assets [Abstract]
Total assets	3,317,696				3,046,692				3,317,696	3,046,692	2,951,723
Diesel Engine Services [Member] \| Reporting Segments [Member]
Revenues [Abstract]
Segment profit (loss)									60,063	42,767	66,386
Total assets	736,129				576,472				736,129	576,472	647,986
Depreciation and amortization									11,463	11,096	12,030
Capital expenditures									7,486	4,658	20,477
Details of "Other" total assets [Abstract]
Total assets	736,129				576,472				736,129	576,472	647,986
Other [Member]
Revenues [Abstract]
Total assets	88,084				59,353				88,084	59,353	53,419
Other segment disclosures [Abstract]
General corporate expenses									(14,896)	(15,728)	(13,294)
Interest expense									(21,461)	(27,872)	(24,385)
Gain (loss) on disposition of assets									781	888	(14)
Other income (expense)									39	368	78
Profit (loss) from other segment									(35,537)	(42,344)	(37,615)
Details of "Other" total assets [Abstract]
General corporate assets	85,545				57,197				85,545	57,197	51,611
Investment in affiliates	2,539				2,156				2,539	2,156	1,808
Total assets	88,084				59,353				88,084	59,353	53,419
Other [Member] \| Reporting Segments [Member]
Revenues [Abstract]
Segment profit (loss)									(35,537)	(42,344)	(37,615)
Total assets	88,084				59,353				88,084	59,353	53,419
Depreciation and amortization									3,830	3,767	3,260
Capital expenditures									7,343	10,605	17,339
Details of "Other" total assets [Abstract]
Total assets	$ 88,084				$ 59,353				$ 88,084	$ 59,353	$ 53,419