Operations by Business Segment and Geographic Area - Revenues and Long-Lived Assets by Location (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 2,271,603	$ 3,062,754	$ 3,659,624
Long-Lived Assets	1,814,301	1,861,938	1,744,498
Foreign [Member]
Segment Reporting Information [Line Items]
Revenues	1,294,259	1,757,317	2,342,279
Long-Lived Assets	786,873	791,097	906,225
Norway [Member]
Segment Reporting Information [Line Items]
Revenues	166,180	250,272	488,789
Long-Lived Assets	277,949	274,868	332,503
Africa [Member]
Segment Reporting Information [Line Items]
Revenues	486,615	659,038	795,229
Long-Lived Assets	234,921	205,440	215,122
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	304,635	367,326	456,804
Long-Lived Assets	102,140	138,327	113,191
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Revenues	196,679	245,978	317,277
Long-Lived Assets	66,279	71,438	90,061
Brazil [Member]
Segment Reporting Information [Line Items]
Revenues	73,280	118,056	185,299
Long-Lived Assets	61,418	57,896	99,269
Other [Member]
Segment Reporting Information [Line Items]
Revenues	66,870	116,647	98,881
Long-Lived Assets	44,166	43,128	56,079
United States [Member]
Segment Reporting Information [Line Items]
Revenues	977,344	1,305,437	1,317,345
Long-Lived Assets	$ 1,027,428	$ 1,070,841	$ 838,273