CONSOLIDATED BALANCE SHEETS Parenthetical (USD $)	Dec. 31, 2013	Dec. 31, 2012
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 2,583,698,000	$ 2,376,170,000
Common Stock, Par Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	200,000,000	200,000,000
Common Stock, Shares, Issued	67,078,853	66,245,816
Common Stock, Shares, Outstanding	67,056,441	66,195,235
Treasury Stock, Shares	22,412	50,581
Assets Held-for-sale [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	7,390,000	20,676,000
Other Capitalized Property Plant and Equipment [Member]
Oil and Gas Property, Successful Effort Method, Accumulated Depreciation, Depletion and Amortization	$ 28,775,000	$ 22,442,000