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Summary of Significant Accounting Policies Other (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Years	Dec. 31, 2013	Dec. 31, 2012
Basis of Presentation and Significant Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	$ 0
Revolving credit facility	166,000,000us-gaap_LineOfCredit	0us-gaap_LineOfCredit
Allowance for Doubtful Accounts Receivable	0	0
Capitalization of Development and Implementation of Internal Use Software	35,000,000	11,200,000
Concentration of Credit Risk and Major Customers [Abstract]
Number of Major Customers	1sm_NumberOfMajorCustomers	3sm_NumberOfMajorCustomers	2sm_NumberOfMajorCustomers
Marketing agreement length for gathering, transportation, and processing through-put commitments	10
Number of Derivative Counterparties	9sm_NumberOfDerivativeCounterparties
Property, Plant and Equipment [Abstract]
Property, Plant, and Equipment, Salvage Value	50,800,000	57,500,000
Inventory, Net [Abstract]
Property, Plant and Equipment, Estimated Useful Lives	three to 30 years
Revenues [Abstract]
Revenue Receipt, Days After Sale, Low End of Range	30
Revenue Receipt, Days After Sale, High End of Range	90
Impairment of Proved Properties [Abstract]
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast	5
Impairment of proved properties	84,480,000us-gaap_ImpairmentOfOilAndGasProperties	172,641,000us-gaap_ImpairmentOfOilAndGasProperties	208,923,000us-gaap_ImpairmentOfOilAndGasProperties
Abandonment and impairment of unproved properties	75,638,000us-gaap_ImpairmentOfLeasehold	46,105,000us-gaap_ImpairmentOfLeasehold	16,342,000us-gaap_ImpairmentOfLeasehold
Regency Gas Services, LLC [Member]
Concentration of Credit Risk and Major Customers [Abstract]
Entity-Wide Revenue, Major Customer, Percentage		26.00%	21.00%
Anadarko Petroleum Company [Member]
Concentration of Credit Risk and Major Customers [Abstract]
Entity-Wide Revenue, Major Customer, Percentage	19.00%	16.00%
Plains Marketing, LP [Member]
Concentration of Credit Risk and Major Customers [Abstract]
Entity-Wide Revenue, Major Customer, Percentage		12.00%	13.00%
Unnamed Major Customer with Related Entities [Member]
Concentration of Credit Risk and Major Customers [Abstract]
Entity-Wide Revenue, Major Customer, Percentage	14.00%
Number of Entities Related to One Unnamed Customer	4
Maximum Percentage of Total Production Revenue for Individual Entity	10.00%
Convertible Debt [Member]
Debt Instruments [Abstract]
Debt Instrument, Convertible, Conversion Price			$ 54.42
Debt Instrument, Principal Amount Denominator for Conversion into Common Stock			$ 1,000
Convertible Debt [Member] \| Convertible Debt [Member]
Debt Instruments [Abstract]
Debt Instrument, Interest Rate, Stated Percentage			3.50%
Debt instrument convertible conversion rate			864,106