Income Taxes - Change in Unrecognized Tax Benefit (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in unrecognized tax benefits
Balance as of January 1	$ 179,255	$ 188,376	$ 201,338
Additions based on tax positions related to the current year			384
Additions for tax positions of prior years	25,119	3,873
Reductions for tax positions of prior years	(171,171)	(11,547)	(9,234)
Settlements		(1,447)	(4,112)
Balance as of December 31	33,203	179,255	188,376
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation			2,000
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations			1,100
Additions based on tax positions related to the current year due to internal restructuring		167,000
Reductions for tax positions for prior years due to expiration of statutes			1,100
Interest and penalties on unrecognized tax benefits	9,700	9,200	7,400
Liability related to unrecognized tax benefit for accrued interest and penalties	500	600	1,400
Canada, Trinidad and U.S
Change in unrecognized tax benefits
Settlements			(6,000)
Colombia, Ecuador, Canada and Montana
Change in unrecognized tax benefits
Settlements			$ (5,000)
Australia Algeria And Mexico
Change in unrecognized tax benefits
Settlements		(2,000)
Unrecognized Tax Benefits, Reduction Resulting from Lapse of Applicable Statute of Limitations		7,200
Reductions for tax positions for prior years due to expiration of statutes		7,200
Trinidad
Change in unrecognized tax benefits
Unrecognized Tax Benefits, Decrease Resulting from Foreign Currency Translation		$ 2,100
Norway
Change in unrecognized tax benefits
Settlements	(12,000)
U.S. Federal
Change in unrecognized tax benefits
Settlements	(9,000)
Egypt
Change in unrecognized tax benefits
Settlements	$ (2,000)