Property And Equipment - Gross Components Of Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment	$ 2,785,778	$ 2,695,772
Vessels
Property, Plant and Equipment [Line Items]
Property and equipment	$ 2,185,409	2,083,267
Vessels | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years
Vessels | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	30 years
ROVs, trenchers and ROVDrills
Property, Plant and Equipment [Line Items]
Property and equipment	$ 284,172	298,227
Estimated useful life	10 years
Machinery, equipment and leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment	$ 316,197	$ 314,278
Machinery, equipment and leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Machinery, equipment and leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	15 years