Debt - Credit Facility (Details)	6 Months Ended
	Jun. 30, 2015 USD ($) redetermindation	Jul. 08, 2014 USD ($)
Line of Credit Facility [Line Items]
Current borrowing capacity	$ 175,000,000
Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 500,000,000
Number of additional redeterminations that may be requested | redetermindation	3
Period of redeterminations	12 months
Amount outstanding under credit facility	$ 0
Federal Funds Rate [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
LIBOR, 3-month [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.00%
Minimum [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Commitment fee on the unused portion of the borrowing base	0.375%
Minimum [Member] | Base Rate [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.50%
Minimum [Member] | LIBOR [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Maximum [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Commitment fee on the unused portion of the borrowing base	0.50%
Maximum [Member] | Base Rate [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.50%
Maximum [Member] | LIBOR [Member] | Wells Fargo [Member] | Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.50%