Consolidated Balance Sheets (Unaudited) (Parenthetical) (USD $) In Thousands, except Share data	Sep. 30, 2011	Dec. 31, 2010
ASSETS
Accumulated depletion on oil and natural gas properties	$ 495,115	$ 423,691
Stockholders' equity:
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	180,000,000	180,000,000
Common stock, shares issued	116,800,125	116,564,182
Common stock, shares outstanding	116,498,651	116,289,180
Treasury stock, shares	301,474	275,002