Leases - Maturities Of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	$ 54,621
2020	66,620
2021	60,121
2022	57,183
2023	39,092
Thereafter	12,904
Total lease payments	290,541
Less: imputed interest	(43,755)
Total operating lease liabilities	246,786
Current operating lease liabilities	55,241	$ 0
Non-current operating lease liabilities	191,545	$ 0
Vessels
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	49,454
2020	60,362
2021	54,611
2022	52,106
2023	34,580
Thereafter	2,470
Total lease payments	253,583
Less: imputed interest	(35,878)
Total operating lease liabilities	217,705
Current operating lease liabilities	50,242
Non-current operating lease liabilities	167,463
Facilities and Equipment
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	5,167
2020	6,258
2021	5,510
2022	5,077
2023	4,512
Thereafter	10,434
Total lease payments	36,958
Less: imputed interest	(7,877)
Total operating lease liabilities	29,081
Current operating lease liabilities	4,999
Non-current operating lease liabilities	$ 24,082