Assets Held-for-Sale and Discontinued Operations Disc Ops (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		21 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Dec. 31, 2017
Discontinued operations
Current liability to discontinued operations	$ 5,762		$ 5,762		$ 5,762	$ 6,074
Income (loss) from Oil & Gas discontinued operations:
Income (loss) from Oil and Gas discontinued operations, net of tax	(13,933)	$ (27,134)	(14,592)	$ (43,077)
Litigation expenses and reserves	1,375	(2,187)	9,652	(577)
Assets Held-for-sale
Income (loss) from Oil & Gas discontinued operations:
Impairment charge	16,500	16,500	16,500	16,500	35,300
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued operations
Undiscounted contractual commitments	5,800		5,800		5,800	11,200
Liability related to discontinued operation	5,800		5,800		$ 5,800	8,500
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations | Accrued liabilities
Discontinued operations
Current liability to discontinued operations						$ 6,100
Oil and Gas
Income (loss) from Oil & Gas discontinued operations:
Litigation expenses and reserves			16,500
Oil and Gas | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income (loss) from Oil & Gas discontinued operations:
Operating revenues	896	1,077	3,512	5,171
Income (loss) from discontinued operations	(652)	(991)	(1,827)	(1,561)
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets (2)	16,511	34,469	16,662	51,028
Less: Income tax expense (benefit)	(3,230)	(8,326)	(3,897)	(9,512)
Income (loss) from Oil and Gas discontinued operations, net of tax	$ (13,933)	$ (27,134)	$ (14,592)	$ (43,077)