Acquisitions and Divestitures Purchase Price Allocation (Details) (USD $) Share data in Millions, except Per Share data, unless otherwise specified	2 Months Ended	3 Months Ended	4 Months Ended	9 Months Ended
	Oct. 30, 2013	Sep. 30, 2013	Apr. 24, 2013	Sep. 30, 2013	Sep. 30, 2012
Acquisitions and Divestitures [Abstract]
Measurement Period Adjustment, Purchase Price Allocation , Proved Oil and Gas Properties		$ 5,400,000
Measurement Period Adjustment, Purchase Price Allocation , Other Assets		2,000,000
Measurement Period Adjustment, Purchase Price Allocation , Accounts Payable and Accrued Expenses		7,400,000
Business Acquisition, Valuation, Net Assets of Acquired Entity			401,000,000
Business Acquisition, Total Consideration Transferred, Net of Proceeds From Investing Partners			380,000,000
Business Acquisition, Purchase Price Adjustments, Effective Date to Date of Acquisition			19,000,000
Stock Issued During Period, Shares, Acquisitions		10
Stock Issued during period, Fair Value per Share, Acquisitions			$ 4.23
Proceeds From Joint Interest Partners Upon Exercise of Preferential Rights Related to the Acquisition		21,000,000
Business Combination, Acquisition Related Costs				2,400,000
BusinessAcquisition, Oil and Gas Properties - Proved			287,465,000
BusinessAcquisitionsPurchasePriceAllocationUnprovedOilandGasProperties			124,232,000
Business Acquisition, Purchase Price Allocation, Current Assets, Receivables			50,726,000
Business Acquisition, Purchase Price Allocation, Current Assets, Prepaid Expense and Other Assets			2,068,000
Business Acquisition, Purchase Price Allocation, Assets Acquired			464,491,000
Business Acquisition, Purchase Price Allocation, Current Liabilities, Accounts Payable			(62,452,000)
Business Acquisition, Purchase Price Allocation, Current Liabilities, Accrued Liabilities			(1,500,000)
Business Acquisition, Purchase Price Allocation, Liabilities Assumed			(63,952,000)
Business Acquisition, Purchase Price Allocation, Assets Acquired (Liabilities Assumed), Net			400,539,000
Cash Payments To Acquire Business, Net of Amounts Received for Preferential Rights		358,239,000
Stock Issued During Period, Value, Acquisitions		42,300,000		42,300,000	0
Business Combination, Consideration Transferred			$ 400,539,000
Business Acquisition, Post Final Settlement Audit Period, Acquiring Entity	30