Assets Held-for-Sale and Discontinued Operations Disc Ops (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Discontinued operations
Current liability to discontinued operations	$ 5,978		$ 6,074
Income (loss) from Oil & Gas discontinued operations:
Income (loss) from Oil and Gas discontinued operations, net of tax	(75)	$ (439)
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations
Discontinued operations
Undiscounted contractual commitments	9,000		11,200
Liability related to discontinued operation	6,900		8,500
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations | Accrued liabilities
Discontinued operations
Current liability to discontinued operations	6,000		$ 6,100
Oil and Gas | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income (loss) from Oil & Gas discontinued operations:
Operating revenues	1,643	2,034
Income (loss) from discontinued operations	(452)	(590)
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets (2)	36	20
Less: Income tax expense (benefit)	(413)	(171)
Income (loss) from Oil and Gas discontinued operations, net of tax	$ (75)	$ (439)