Subsequent Events (Details) (USD $)	9 Months Ended						0 Months Ended			0 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Oct. 24, 2014 Senior Secured Revolving Credit Facility [Member]	Oct. 07, 2014 Senior Secured Revolving Credit Facility [Member]	Sep. 30, 2014 Senior Secured Revolving Credit Facility [Member]	Apr. 10, 2014 Senior Secured Revolving Credit Facility [Member]	Oct. 30, 2014 Seven Point Five Percent Senior Notes Issued 2014 [Member] [Member]	Oct. 30, 2014 Seven Point Five Percent Senior Notes Issued 2014 [Member] [Member]	Sep. 30, 2014 Seven Point Five Percent Senior Notes Issued 2014 [Member] [Member]	Feb. 16, 2015 Eagle Ford Shale Transaction [Member]	Oct. 24, 2014 Eagle Ford Shale Transaction [Member]	Oct. 24, 2014 Eagle Ford Shale Transaction [Member]	Sep. 30, 2014 Eagle Ford Shale Transaction [Member]
Subsequent Event [Line Items]
Letter of Credit Facility, Sublimit				$ 30,000,000	$ 15,000,000
Line of credit facility, current borrowing capacity			800,000,000	675,000,000	570,000,000	470,000,000
Line of Credit Facility, Elected Borrowing Capacity			685,000,000	585,000,000
Line of Credit Facility, Availability of Issuances of Additional Senior Notes				350,000,000
Adjusted Purchase Price for Acquisition of Oil and Gas Property												243,000,000
Sale Price of Oil and Gas Property and Equipment											250,000,000
Payments to Acquire Oil and Gas Property										150,000,000	93,000,000
Percentage of Working Interest Prior to Acquisition													75.00%
Percentage of Working Interest Subsequent to Acquisition												100.00%
Long Term Debt								300,000,000
Debt Instrument, Interest Rate, Stated Percentage									7.50%
Senior Notes Issuance Price Percentage of Principal Amount in Private Placement								100.50%
Proceeds from Issuance of Long-term Debt	$ 646,000,000	$ 437,000,000					$ 299,813,000