Operations by Business Segment and Geographic Area - Revenues and Long-Lived Assets by Location (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]
Revenues	$ 3,659,624	$ 3,287,019	$ 2,782,604
Long-Lived Assets	1,744,498	1,642,363	1,522,287
Africa [Member]
Segment Reporting Information [Line Items]
Revenues	795,229	696,202	505,541
Long-Lived Assets	215,122	186,865	141,927
Foreign [Member]
Segment Reporting Information [Line Items]
Revenues	2,342,279	2,180,381	1,827,376
Long-Lived Assets	906,225	950,959	914,715
Norway [Member]
Segment Reporting Information [Line Items]
Revenues	488,789	461,915	461,863
Long-Lived Assets	332,503	429,603	474,408
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues	456,804	383,397	334,319
Long-Lived Assets	113,191	99,250	85,434
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Revenues	317,277	335,129	290,821
Long-Lived Assets	90,061	83,885	65,012
Brazil [Member]
Segment Reporting Information [Line Items]
Revenues	185,299	213,282	164,660
Long-Lived Assets	99,269	112,840	113,829
Other [Member]
Segment Reporting Information [Line Items]
Revenues	98,881	90,456	70,172
Long-Lived Assets	56,079	38,516	34,105
United States [Member]
Segment Reporting Information [Line Items]
Revenues	1,317,345	1,106,638	955,228
Long-Lived Assets	$ 838,273	$ 691,404	$ 607,572