Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, par value	$ 0.01	$ 0.01
Unevaluated costs of oil and gas properties	$ 21,377	$ 18,803
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	191,487,376	187,802,994
Treasury stock, shares	8,378,865	7,444,372