Income Taxes (Schedule of Deferred Tax Assets and Liabilities) (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Deferred tax asset:
Deferred compensation	$ 1,861	$ 2,401
Asset retirement obligation	53,140	84,941
Net operating loss and capital loss carryforward	422,828	423,374
Unrealized loss on embedded derivative instruments		1,265
Property, plant and equipment	19,633	14,086
Inventory / other	769	2,185
Total deferred tax assets	498,231	528,252
Less valuation allowance	(335,251)	(103,171)
Total deferred tax assets after valuation allowance	162,980	425,081
Deferred tax liabilities:
Property, plant and equipment	(192,847)	(526,274)
Petroleum revenue tax, net of tax benefit	(16,100)	(17,967)
Debt discount		(471)
Total deferred tax liabilities	(208,947)	(544,712)
Net deferred tax liability	$ (45,967)	$ (119,631)