Fair Value Measurements Proved and Unproved Oil and Gas Properties and Other Property and Equipment (Details) - USD ($) $ in Thousands		3 Months Ended
	Mar. 31, 2018	Mar. 31, 2018	Mar. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Proved Oil and Gas Properties		$ 0	$ 0
Abandonment and impairment of unproved oil and gas properties		5,625	0
Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down		$ 24,100	359,600
Divide County Disposal Group [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Disposal Group, Not Discontinued Operation, Loss (Gain) on Write-down			$ 359,600
Oil and Gas Properties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5 years
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%
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%