Segment Data (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Segment Data [Abstract]
Number of reportable segments | Segment									2
Revenues [Abstract]
Revenues									$ 2,970,697	$ 2,214,418	$ 1,770,673
Segment profit (loss)	$ (30,292)	$ 57,066	$ 44,854	$ 42,531	$ (58,860)	$ 47,861	$ 43,015	$ 40,998	114,159	73,014	227,746
Total assets	5,871,594				5,127,427				5,871,594	5,127,427	4,289,895
Depreciation and amortization									224,972	202,881	200,917
Capital expenditures									301,861	177,222	231,066
Other segment disclosures [Abstract]
Interest expense	(12,191)	(12,345)	(12,540)	(9,780)	(7,162)	(5,388)	(4,465)	(4,457)	(46,856)	(21,472)	(17,690)
Impairment of long-lived assets	(82,705)				(105,712)				(82,705)	(105,712)	0
Impairment of goodwill									(2,702)	0	0
Lease Cancellation Costs									(2,403)	0	0
Gain (loss) on disposition of assets	(390)	18	442	1,898	(4,288)	(159)	(139)	99	1,968	(4,487)	(127)
Nonoperating expense	1,140	1,454	1,541	1,591	902	320	228	(589)
Earnings before taxes on income	(30,292)	$ 57,066	$ 44,854	$ 42,531	(58,860)	$ 47,861	$ 43,015	$ 40,998	114,159	73,014	227,746
Details of "Other" total assets [Abstract]
Investment in affiliates	2,495				1,890				2,495	1,890
Marine Transportation [Member]
Revenues [Abstract]
Revenues									1,483,143	1,324,106	1,471,893
Distribution and Services [Member]
Revenues [Abstract]
Revenues									1,487,554	890,312	298,780
Other [Member]
Revenues [Abstract]
Segment profit (loss)									(162,562)	(149,012)	(34,775)
Total assets	72,664				75,243				72,664	75,243	52,676
Depreciation and amortization									3,316	3,596	3,793
Capital expenditures									6,166	6,715	7,728
Other segment disclosures [Abstract]
General corporate expenses									(35,590)	(18,202)	(15,024)
Interest expense									(46,856)	(21,472)	(17,690)
Impairment of long-lived assets									(82,705)	(105,712)	0
Impairment of goodwill									(2,702)	0	0
Lease Cancellation Costs									(2,403)	0	0
Gain (loss) on disposition of assets									1,968	(4,487)	(127)
Nonoperating expense									5,726	861	(1,934)
Earnings before taxes on income									(162,562)	(149,012)	(34,775)
Details of "Other" total assets [Abstract]
General corporate assets	70,169				73,353				70,169	73,353	50,054
Investment in affiliates	2,495				1,890				2,495	1,890	2,622
Total other assets	72,664				75,243				72,664	75,243	52,676
Reportable Segments [Member] | Marine Transportation [Member]
Revenues [Abstract]
Revenues									1,483,143	1,324,106	1,471,893
Segment profit (loss)									147,416	135,547	259,453
Total assets	4,145,294				3,485,099				4,145,294	3,485,099	3,613,951
Depreciation and amortization									182,307	178,898	184,291
Capital expenditures									284,953	165,421	217,423
Other segment disclosures [Abstract]
Earnings before taxes on income									147,416	135,547	259,453
Reportable Segments [Member] | Distribution and Services [Member]
Revenues [Abstract]
Revenues									1,487,554	890,312	298,780
Segment profit (loss)									129,305	86,479	3,068
Total assets	$ 1,653,636				$ 1,567,085				1,653,636	1,567,085	623,268
Depreciation and amortization									39,349	20,387	12,833
Capital expenditures									10,742	5,086	5,915
Other segment disclosures [Abstract]
Earnings before taxes on income									129,305	86,479	3,068
Intersegment Eliminations [Member]
Revenues [Abstract]
Revenues									29,363	20,717	24,672
Segment profit (loss)									29,363	2,072	2,467
Other segment disclosures [Abstract]
Earnings before taxes on income									$ 29,363	$ 2,072	$ 2,467