Liquidity and Capital Resources (Details) (USD $)	3 Months Ended	0 Months Ended
	Mar. 31, 2015	Mar. 24, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Available cash	$ 11,941,000		$ 11,557,000	$ 14,648,000	$ 33,163,000
Contractual obligation due on 2015	143,500,000
Contractual obligation due on 2016	132,000,000
Contractual obligation due on 2017	131,200,000
Interest payments on the senior notes due on 2015	387,800,000
Interest payments on the senior notes due on 2016	355,400,000
Interest payments on the senior notes due on 2017	355,400,000
Liquidity Sufficiency
Cash payment on derivative contract settlement	52,600,000
Financial Ratio Covenants
Net consolidated indebtedness to EBITDA ratio	3.7
Current Ratio	1.0
Amount of current assets exceeded its current liabilities	1,500,000
Borrowing Base Redetermination
Net consolidated indebtedness to EBITDA ratio	3.7
Cross Default Provisions
Minimum effective borrowing base under credit facility	5.00%
Minimum indebtedness of senior notes including principal amount	50,000,000
Credit Facility
Availability under the facility	88,400,000
Credit Facility | Sixth Amendment
Borrowing Base Redetermination
Borrowing base		525,000,000
Credit Facility | Sixth Amendment | Minimum
Financial Ratio Covenants
Net consolidated indebtedness to EBITDA ratio	4.0
Borrowing Base Redetermination
Net consolidated indebtedness to EBITDA ratio	4.0
Property under mortgage (as a percent)		80.00%
Credit Facility | Sixth Amendment | Maximum
Financial Ratio Covenants
Net consolidated indebtedness to EBITDA ratio	4.5
Borrowing Base Redetermination
Net consolidated indebtedness to EBITDA ratio	4.5
Property under mortgage (as a percent)		90.00%
2020 Senior Notes
Liquidity Sufficiency
Periodic interest payment amount on due dates	32,000,000
2021 Senior Notes
Liquidity Sufficiency
Periodic interest payment amount on due dates	$ 32,000,000