Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014
Consolidated Balance Sheets [Abstract]
Unevaluated properties not being amortized	$ 435.4	$ 679.1	$ 498.7	$ 908.5	$ 908.5
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares authorized	1,000,000	1,000,000	1,000,000	1,000,000	1,000,000
Preferred stock, shares issued	0	0	0	0	0
Preferred stock, shares outstanding	0	0	0	0	0
Common stock, par value	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001
Common stock, shares authorized	75,000,000	75,000,000	75,000,000	75,000,000	75,000,000
Common stock, shares issued	1,000	1,000	1,000	1,000	1,000
Common stock, shares outstanding	1,000	1,000	1,000	1,000	1,000