Fair Value Measurements Proved and Unproved Oil and Gas Properties (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant and Equipment, Net		$ 4,364,694		$ 4,364,694		$ 4,950,280
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast				5 years
Impairment of Proved Oil and Gas Properties		8,049	$ 55,990	$ 277,834	$ 124,430	468,700
Abandonment and impairment of unproved properties		$ 3,568	$ 6,600	$ 5,917	$ 24,046	78,600
Impairment of Long-Lived Assets Held-for-use						49,400
Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant and Equipment, Net	[1]					$ 124,813
Oil and Gas Properties [Member] | Minimum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate				10.00%		10.00%
Oil and Gas Properties [Member] | Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Inputs, Discount Rate				15.00%		15.00%

[1] This represents a non-financial asset that is measured at fair value on a nonrecurring basis.