Commitments And Contingencies And Other Matters - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Commitments And Contingencies [Line Items]
Total investment	$ 2,727,760	$ 2,695,772
Q7000
Commitments And Contingencies [Line Items]
Total investment	$ 323,500
Q7000 | Contract Signing
Commitments And Contingencies [Line Items]
Percentage of contract price	20.00%
Q7000 | Due 2016
Commitments And Contingencies [Line Items]
Percentage of contract price	20.00%
Q7000 | Due December 2017
Commitments And Contingencies [Line Items]
Percentage of contract price	20.00%
Q7000 | Due December 31, 2018
Commitments And Contingencies [Line Items]
Percentage of contract price	20.00%
Q7000 | Vessel Delivery
Commitments And Contingencies [Line Items]
Percentage of contract price	20.00%
Q7000 | Shipyard
Commitments And Contingencies [Line Items]
Total investment	$ 207,600