Fair Value Measurements Proved and Unproved Oil and Gas Properties (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2016		Mar. 31, 2015	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant and Equipment, Net	$ 4,603,779			$ 4,950,280
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5 years
Impairment of Proved Oil and Gas Properties	$ 269,785		$ 55,526
Abandonment and impairment of unproved properties	2,311		11,627
Impairment of Long-Lived Assets Held-for-use				49,400
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down	68,300		$ 30,000
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	$ 439,942	[1]		$ 124,813	[2]
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.

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