Business Segment Information - Revenue By Geographical Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total net revenues	$ 163,266	$ 163,260	$ 150,329	$ 104,528	$ 128,031	$ 161,245	$ 107,267	$ 91,039	$ 581,383	$ 487,582	$ 695,802
United States [Member]
Segment Reporting Information [Line Items]
Total net revenues									283,933	298,279	298,391
North Sea [Member]
Segment Reporting Information [Line Items]
Total net revenues									159,961	137,313	263,438
United Kingdom [Member]
Segment Reporting Information [Line Items]
Total net revenues									156,000	123,600	187,700
Brazil [Member]
Segment Reporting Information [Line Items]
Total net revenues									70,710	2,543	28,487
Other [Member]
Segment Reporting Information [Line Items]
Total net revenues									$ 66,779	$ 49,447	$ 105,486