Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
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	$ 230,719	$ 221,605
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	184,764,736	183,994,879
Treasury stock, shares	7,441,757	6,698,640