Fair Value Measurements Proved and Unproved Oil and Gas Properties (Details) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2017		Mar. 31, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Property, Plant and Equipment, Net	$ 5,450,120			$ 6,081,354
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5 years
Impairment of Proved Oil and Gas Properties	$ 0		$ 269,785
Abandonment and impairment of unproved properties	0		2,311
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down			68,300
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	$ 443,772	[1]		$ 88,205	[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%
Divide County Divestiture 2017 [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Proved Oil and Gas Properties	$ 359,600
Abandonment and impairment of unproved properties			$ 1,600

[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.