Debt - Senior Notes (Details) (USD $)				9 Months Ended
	Sep. 30, 2014 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member]	Dec. 31, 2013 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member]	Sep. 18, 2013 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member]	Sep. 30, 2014 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] 12-month period beginning October 1, 2016 [Member]	Sep. 30, 2014 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] 12-month period beginning October 1, 2017 [Member]	Sep. 30, 2014 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] 12-month period beginning October 1, 2018 [Member]	Sep. 30, 2014 Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] 12-month period beginning October 1, 2019 and thereafter [Member]	Sep. 30, 2014 Make-whole premium option [Member] Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] Period prior to October 1, 2016 [Member]	Sep. 30, 2014 Net cash proceeds of certain equity offerings [Member] Senior Notes [Member] Senior Unsecured Notes due 2021 [Member] Period prior to October 1, 2016 [Member]	Sep. 19, 2013 Midland County, Texas [Member] acre
Debt Instrument [Line Items]
Aggregate principal amount			$ 450,000,000
Stated interest rate	7.625%	7.625%	7.625%
Acres of oil and gas property, mineral interest, gross										14,804
Acres of oil and gas property, mineral interest, net										12,687
Redemption price, expressed as percentage of principal amount				105.719%	103.813%	101.906%	100.00%	100.00%	107.625%
Maximum percent of aggregate principal amount redeemable									35.00%
Minimum required principal amount to remain outstanding subsequent to redemption									65.00%
Number of days within closing date redemption can occur									120 days