Revenue - Revenue by Geographic Area (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenue by Geographic Area [Line Items]
Revenues	$ 495,781	$ 493,886	$ 478,674	$ 989,667	$ 895,087
Africa [Member]
Revenue by Geographic Area [Line Items]
Revenues	61,390	87,106	61,966	148,496	117,053
United Kingdom [Member]
Revenue by Geographic Area [Line Items]
Revenues	65,058	53,298	50,999	118,356	96,318
Norway [Member]
Revenue by Geographic Area [Line Items]
Revenues	60,252	42,466	51,827	102,718	90,869
Asia Pacific [Member]
Revenue by Geographic Area [Line Items]
Revenues	43,123	41,426	43,448	84,549	82,394
Brazil [Member]
Revenue by Geographic Area [Line Items]
Revenues	23,658	17,763	13,461	41,421	32,289
Other Geographical [Member]
Revenue by Geographic Area [Line Items]
Revenues	28,334	21,222	14,811	49,556	34,450
Non-US [Member]
Revenue by Geographic Area [Line Items]
Revenues	281,815	263,281	236,512	545,096	453,373
UNITED STATES
Revenue by Geographic Area [Line Items]
Revenues	$ 213,966	$ 230,605	$ 242,162	$ 444,571	$ 441,714