Assets Held-for-Sale and Discontinued Operations Disc Ops (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Discontinued operations
Current liability to discontinued operations	$ 5,457		$ 5,457		$ 6,074
Income (loss) from Oil & Gas discontinued operations:
Income (loss) from Oil and Gas discontinued operations, net of tax	(584)	$ (15,504)	(659)	$ (15,943)
Litigation expenses and reserves	4,677	789	8,277	1,610
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued operations
Undiscounted contractual commitments	7,000		7,000		11,200
Liability related to discontinued operation	5,500		5,500		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	973	2,060	2,616	4,094
Income (loss) from discontinued operations	(723)	20	(1,175)	(570)
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets (2)	115	16,539	151	16,559
Less: Income tax expense (benefit)	(254)	(1,015)	(667)	(1,186)
Income (loss) from Oil and Gas discontinued operations, net of tax	$ (584)	$ (15,504)	$ (659)	$ (15,943)