Condensed Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Sep. 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	$ 218,398	$ 221,605
Common stock, shares authorized	400,000,000	400,000,000
Common stock, shares issued	187,222,654	183,994,879
Treasury stock, shares	7,444,372	6,698,640