Commitments (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Commitments and Contingencies Disclosure [Line Items]
Operating lease rental payments due in 2019	$ 188,600
Operating lease rental payments due in 2020	88,900
Operating lease rental payments due in 2021	61,900
Operating lease rental payments due in 2022	27,600
Operating lease rental payments due in 2023	15,600
Rental expenses for non-cancellable lease, including contingent payments	75,300	$ 72,600	$ 77,500
Commitments for capital expenditures	383,100
Malaysia [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	103,000
Kaybob Duvernay Lands, Alberta [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	60,000
Eagle Ford Shale [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	31,400
Mexico [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	14,700
Gulf Of Mexico [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	$ 165,200
Rig contract cancellation period	30 days
Vietnam [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	$ 8,800
Drilling Rigs And Associated Equipment [Member]
Commitments and Contingencies Disclosure [Line Items]
Commitments for capital expenditures	57,900
Processing Production Handling and Transportation Services [Member]
Commitments and Contingencies Disclosure [Line Items]
Operating lease rental payments due in 2019	116,800
Operating lease rental payments due in 2020	128,000
Operating lease rental payments due in 2021	145,300
Operating lease rental payments due in 2022	136,200
Operating lease rental payments due in 2023	123,700
Processing and transportation charges	$ 52,200	$ 53,800	$ 50,300