Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017
Revenue by Geographic Area [Line Items]
Revenues	$ 416,413	$ 484,175	$ 446,176
Africa [Member]
Revenue by Geographic Area [Line Items]
Revenues	55,087	43,026	80,512
United Kingdom Member
Revenue by Geographic Area [Line Items]
Revenues	45,319	46,643	66,746
Norway Member
Revenue by Geographic Area [Line Items]
Revenues	39,042	49,747	29,800
Asia Pacific [Member]
Revenue by Geographic Area [Line Items]
Revenues	38,946	46,310	45,867
Brazil Member
Revenue by Geographic Area [Line Items]
Revenues	18,828	16,801	10,692
Segment, Geographical, Groups of Countries, Group Three [Member]
Revenue by Geographic Area [Line Items]
Revenues	19,639	26,823	14,604
Segment, Geographical, Groups of Countries, Foreign [Member]
Revenue by Geographic Area [Line Items]
Revenues	216,861	229,350	248,221
UNITED STATES
Revenue by Geographic Area [Line Items]
Revenues	$ 199,552	$ 254,825	$ 197,955