Fair Value Measurements (Details) (USD $)																																							3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2013 Recurring basis Level 1		Dec. 31, 2012 Recurring basis Level 1		Dec. 31, 2013 Recurring basis Level 1 Not Designated as Hedging Instrument [Member]		Dec. 31, 2012 Recurring basis Level 1 Not Designated as Hedging Instrument [Member]		Dec. 31, 2013 Recurring basis Level 2		Dec. 31, 2012 Recurring basis Level 2		Dec. 31, 2013 Recurring basis Level 2 Not Designated as Hedging Instrument [Member]		Dec. 31, 2012 Recurring basis Level 2 Not Designated as Hedging Instrument [Member]		Dec. 31, 2013 Recurring basis Fair Value, Inputs, Level 3 [Member]		Dec. 31, 2012 Recurring basis Fair Value, Inputs, Level 3 [Member]		Dec. 31, 2013 Recurring basis Fair Value, Inputs, Level 3 [Member] Not Designated as Hedging Instrument [Member]		Dec. 31, 2012 Recurring basis Fair Value, Inputs, Level 3 [Member] Not Designated as Hedging Instrument [Member]		Dec. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Level 1		Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 1		Dec. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Level 2		Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Level 2		Dec. 31, 2013 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 3 [Member]		Dec. 31, 2012 Fair Value, Measurements, Nonrecurring [Member] Fair Value, Inputs, Level 3 [Member]		Mar. 31, 2011 Net Profit Plan liability [Member]	Dec. 31, 2013 Net Profit Plan liability [Member]
Financial assets and liabilities measured at fair value on a recurring basis
Percent Decrease in Discount Rate for Sensitivity Analysis																																								1.00%
Payment to Settle, Net Profit Plan Liability																																							$ 2,600,000
Assets:
Derivatives							0	[1]	0	[1]					52,510,000	[1]	54,339,000	[1]					0	[1]	0	[1]
Derivative Asset, Fair Value, Amount Offset Against Collateral	52,510,000	54,339,000
Proved oil and gas properties	5,637,462,000	5,401,684,000																									0	[2]	0	[2]	0	[2]	0	[2]	62,178,000	[2]	209,959,000	[2]
Unproved Oil and Gas Property, Successful Efforts Method, Fair Value	271,100,000	175,287,000																									0	[2]	0	[2]	0	[2]	0	[2]	3,280,000	[2]	42,765,000	[2]
Oil and gas properties held for sale, net of accumulated depletion, depreciation and amortization of $7,390 in 2013 and $20,676 in 2012	19,072,000	33,620,000																									0	[2]			0	[2]			650,000	[2]
Liabilities [Abstract]
Derivative Liability, Fair Value, Gross Liability							0	[1]	0	[1]					31,020,000	[1]	15,644,000	[1]					0	[1]	0	[1]
Net Profits Plan liability	$ 56,985,000	$ 78,827,000	$ 0	[1]	$ 0	[1]					$ 0	[1]	$ 0	[1]					$ 56,985,000	[1]	$ 78,827,000	[1]

[1] This represents a financial asset or liability that is measured at fair value on a recurring basis.

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