Investments, At Equity, And Advances To 50% Or Less Owned Companies (Narrative) (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) equipment	Dec. 31, 2016 USD ($) equipment	Dec. 31, 2015 USD ($) equipment	Dec. 31, 2014 USD ($)	Jun. 30, 2017	Dec. 02, 2016	Nov. 30, 2016 USD ($)	Jun. 01, 2015
Schedule of Equity Method Investments [Line Items]
Cumulative undistributed net earnings of 50% or less owned companies accounted for by the equity method included in the Company's consolidated retained earnings		$ (40,100)	$ (35,000)
Proceeds from Issuance of Secured Debt			8,000	$ 1,700
Proceeds on the sale of a controlling interest in a subsidiary		5,000	0	0
Letters of Credit Outstanding, Amount	$ 27,200
Proceeds from Equity Method Investment, Distribution		15,568	9,519	46,306
Asset Impairment Charges		400	1,100
Trailer Bridge Inc [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of Advances				(18,700)
Related Party Transaction, Revenues from Transactions with Related Party			$ 300	800
Equity Method Investment, Ownership Percentage			55.30%
Payments for Advance to Affiliate		2,000	$ 1,700
Proceeds from Collection of Advance to Affiliate		(6,000)
Business Combination, Separately Recognized Transactions, Net Gains and Losses			(2,200)
RF Vessel Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds on the sale of a controlling interest in a subsidiary		$ 1,900
Equity Method Investment, Ownership Percentage		50.00%
Golfo de Mexico [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		$ 300
Proceeds on the sale of a controlling interest in a subsidiary		3,100
Equity Method Investment, Ownership Percentage						50.00%
Proceeds from Equity Method Investment, Distribution, Return of Capital		300
KSM [Member]
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Contributions	$ 300
Related Party Transaction, Revenues from Transactions with Related Party		300
Equity Method Investment, Ownership Percentage	50.00%
SeaJon
Schedule of Equity Method Investments [Line Items]
Proceeds from Equity Method Investment, Distribution, Return of Capital		3,500	600	600
Proceeds from Equity Method Investment, Distribution		12,500
Sea-Access [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party			500	1,000
Proceeds from Equity Method Investment, Distribution, Return of Capital			2,000	4,400
Partners' Capital Account, Return of Capital			8,400	8,300
SeaJon II [Member]
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Contributions				1,000
Related Party Transaction, Revenues from Transactions with Related Party			100	100
Partners' Capital Account, Return of Capital				300
Business Combination, Separately Recognized Transactions, Net Gains and Losses			1,900
SCFCo Holdings
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Contributions		400		800	$ 18,000
Repayments of Advances				(14,000)
Related Party Transaction, Revenues from Transactions with Related Party		100	100	200
Equity Method Investment, Other than Temporary Impairment			7,700	21,500
Equity Method Investment, Difference Between Carrying Amount and Underlying Equity		26,500
Payments for Advance to Affiliate		2,500	1,800
Proceeds from Collection of Advance to Affiliate		(1,700)
Asset Impairment Charges				21,500
Advanced to joint ventures		30,300
Bunge-SCF Grain [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of Advances				(2,000)
Related Party Transaction, Revenues from Transactions with Related Party		1,100	1,000	1,000
Related party transaction expense		7,200	7,200	10,800
Advanced to joint ventures		7,000
SCF Bunge Marine [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		38,700	35,000	41,700
Related party transaction expense		41,400	40,200	47,900
Proceeds from Equity Method Investment, Distribution, Return of Capital		100	2,500	4,000
Witt O'Brien's do Brazil [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Equity Method Investment, Distribution, Return of Capital		100	100	100
Dorian LPG [Member]
Schedule of Equity Method Investments [Line Items]
Business Combination, Separately Recognized Transactions, Net Gains and Losses				32,300
Hawker Pacific Airservices Limited [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		300	300	300
Letters of Credit Outstanding, Amount		6,500
VA&E [Member]
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Contributions				3,500
Repayments of Advances			$ (1,100)
Equity Method Investment, Other than Temporary Impairment	$ 900
Equity Method Investment, Ownership Percentage			41.30%						81.10%
Advanced to joint ventures		7,600
Line of Credit Facility, Maximum Borrowing Capacity			$ 3,500					$ 6,000
Proceeds from Unsecured Lines of Credit		3,500	10,000	15,000
Repayments of Long-term Lines of Credit			12,400	11,500
Avion Pacific Limited [Member]
Schedule of Equity Method Investments [Line Items]
Repayments of Advances				(3,000)
Payments for Advance to Affiliate		1,000	3,000
Proceeds from Collection of Advance to Affiliate		(4,000)
Cleancor [Member]
Schedule of Equity Method Investments [Line Items]
Payments for Advance to Affiliate				2,000
Advanced to joint ventures		1,900
Other Corporate Joint Ventures [Member]
Schedule of Equity Method Investments [Line Items]
Partners' Capital Account, Contributions			$ 800	$ 200
Proceeds from Collection of Advance to Affiliate		(400)
Advanced to joint ventures		$ 2,400
Inland River Towboats [Member]
Schedule of Equity Method Investments [Line Items]
Number Of Equipments Acquired | equipment		3	2	9
Inland River Dry Cargo Barges [Member]
Schedule of Equity Method Investments [Line Items]
Number Of Equipments Acquired | equipment		0	46	0
U.S.-flag Harbor Tugs [Member]
Schedule of Equity Method Investments [Line Items]
Number Of Equipments Acquired | equipment		1	1	0
U.S.-flag Harbor Tugs [Member] | Trailer Bridge Inc [Member]
Schedule of Equity Method Investments [Line Items]
Related Party Transaction, Revenues from Transactions with Related Party		$ 3,100	$ 3,000	$ 400
SeaJon II [Member]
Schedule of Equity Method Investments [Line Items]
Business Acquisition, Percentage of Voting Interests Acquired							50.00%
Payments to Acquire Businesses, Gross			3,400
SeaJon II [Member] | U.S.-flag Harbor Tugs [Member]
Schedule of Equity Method Investments [Line Items]
Number Of Equipments Acquired | equipment		1
Subordinated Debt [Member] | VA&E [Member]
Schedule of Equity Method Investments [Line Items]
Advanced to joint ventures	$ 3,500		$ 3,500	$ 1,000
Long-term Debt [Member] | VA&E [Member]
Schedule of Equity Method Investments [Line Items]
Advanced to joint ventures								$ 1,100