Acquisitions and Divestitures (Narrative) (Details) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2015 USD ($) Rate	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) Rate	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2014
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net		$ 779,000	$ 1,000	$ 782,000	$ 11,000
Equity Method Investment, Ownership Percentage | Rate		50.10%		50.10%
Equity Method Investment, Net Sales Proceeds				$ 1,000,000
Equity Method Investment, Realized Gain (Loss) on Disposal				778,000
Idle Rig Expense	[1]	$ 22,000	2,000	73,000	2,000
Proceeds from Sale of Productive Assets				556,000	855,000
Impairment of oil and gas properties		72,000	$ 0	210,000	0
Sendero [Member]
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net					1,000
Proceeds from Divestiture of Interest in Consolidated Subsidiaries					31,000
Idle Rig Expense		$ 10,000		30,000
Gaines Dawson [Member]
Acquisitions and Divestitures [Line Items]
Gain (loss) on disposition of assets, net					2,000
Proceeds from Sale of Productive Assets					$ 72,000
Lease Contract through Year 2 [Member]
Acquisitions and Divestitures [Line Items]
Drilling rigs leased							12
Lease Contract for Year 3 [Member]
Acquisitions and Divestitures [Line Items]
Drilling rigs leased							8
Discontinued Operations [Member] | Hugoton field [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets						$ 328,000
Discontinued Operations [Member] | Pioneer Alaska [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets						267,000
Discontinued Operations [Member] | Barnett Shale Field [Member]
Acquisitions and Divestitures [Line Items]
Proceeds from Sale of Productive Assets						$ 150,000
Proceeds Received Current Year [Member]
Acquisitions and Divestitures [Line Items]
Equity Method Investment, Net Sales Proceeds				530,000
Proceeds To Be Received In Future Year [Member] [Member]
Acquisitions and Divestitures [Line Items]
Equity Method Investment, Net Sales Proceeds				$ 500,000

[1] Primarily represents expenses attributable to idle drilling rig fees, which are not chargeable to joint operations.