Revenue - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended			9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue by Geographic Area [Line Items]
Revenues	$ 497,647	$ 495,781	$ 519,300	$ 1,487,314	$ 1,414,387
Africa [Member]
Revenue by Geographic Area [Line Items]
Revenues	73,901	61,390	51,669	222,397	168,722
United Kingdom [Member]
Revenue by Geographic Area [Line Items]
Revenues	61,914	65,058	56,769	180,270	153,087
Norway [Member]
Revenue by Geographic Area [Line Items]
Revenues	59,875	60,252	51,952	162,593	142,820
Asia Pacific [Member]
Revenue by Geographic Area [Line Items]
Revenues	42,662	43,123	39,764	127,211	122,158
Brazil [Member]
Revenue by Geographic Area [Line Items]
Revenues	25,404	23,658	14,554	66,825	46,844
Other Geographical [Member]
Revenue by Geographic Area [Line Items]
Revenues	14,178	28,334	45,898	63,734	80,348
Non-US [Member]
Revenue by Geographic Area [Line Items]
Revenues	277,934	281,815	260,606	823,030	713,979
UNITED STATES
Revenue by Geographic Area [Line Items]
Revenues	$ 219,713	$ 213,966	$ 258,694	$ 664,284	$ 700,408