Assets Held-for-Sale and Discontinued Operations Disc Ops (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Income (loss) from discontinued operations
Income (loss) from discontinued operations, net of tax	$ (984)	$ 5,025	$ (1,910)	$ 4,208
Gas transport and processing
Contracts for gas transport and processing
Contractual Obligation	21,400		21,400		$ 23,300
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations
Contracts for gas transport and processing
Recorded contractual commitments			15,200		16,100
Gas transport and processing | Disposal Group, Held-for-sale, Not Discontinued Operations | Accrued liabilities
Contracts for gas transport and processing
Recorded contractual commitments			5,600		$ 5,200
Oil and Gas | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income (loss) from discontinued operations
Operating revenues	384	855	761	2,305
Income (loss) from discontinued operations	(1,335)	(1,129)	(2,661)	(2,515)
Less: Impairment charges or other (gains) and losses on sale of wholly owned assets and obligations		1,031		1,031
Less: Income tax expense (benefit)	(351)	(7,185)	(751)	(7,754)
Income (loss) from discontinued operations, net of tax	$ (984)	$ 5,025	$ (1,910)	$ 4,208