Assets Held for Sale and Discontinued Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Discontinued operations
Undiscounted contractual commitments	$ 17,200				$ 23,300				$ 17,200	$ 23,300
Liability related to discontinued operation	12,500				16,100				12,500	16,100
Current liability to discontinued operations	5,462				5,197				5,462	5,197
Recorded Supply Obligation									5,500	5,200
Operating revenues
Operating revenues									2,859	3,212	$ 13,143
Income (loss) from discontinued operations
Income (loss) from discontinued operations, net of tax	(4,266)	$ (12,187)	$ (984)	$ (926)	(1,730)	$ (45,275)	$ 5,025	$ (817)	(18,363)	(42,797)	21
Long-term deferred income taxes	9,495				29,326				9,495	29,326
Cash proceeds from sale of businesses in Alaska											35,100
Receivables held for sale											27,000
Proceed from sale of working interest											600,000
Sale of business
Gain on sale of oil and gas operations											22,200
Other long-term assets	$ 595,783				$ 452,305				595,783	452,305
Charges to reserve for amounts associated with retained interest in properties									22,400
Assets Held-for-sale
Income (loss) from discontinued operations
Impairment charge									15,400	51,000
Impairment of note receivable									3,100
Oil and Gas
Income (loss) from discontinued operations
Income (loss) from discontinued operations									(3,978)	(5,003)	(1,840)
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets and obligations									19,445	49,890	(1,313)
Less: Income tax expense (benefit)									(5,060)	(14,455)	(548)
Income (loss) from discontinued operations, net of tax									$ (18,363)	(40,438)	$ 21
Rig Services
Income (loss) from discontinued operations
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets and obligations										3,146
Less: Income tax expense (benefit)										(787)
Income (loss) from discontinued operations, net of tax										$ (2,359)