Acquisitions and Divestures (Details) (USD $)	6 Months Ended		0 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jan. 31, 2012 Nevada Assets	Apr. 13, 2012 Wolfberry Acquisition acre	May 25, 2011 Wolfberry Acquisition acre
Acquisitions
Interests acquired in oil and natural gas properties (in net acres)				2,000	6,000
Purchase price paid, net of customary post-closing adjustments	$ 24,851,000	$ 145,461,000		$ 14,900,000	$ 128,400,000
Divestures
Proceeds from sale of assets	15,722,000	0	15,600,000
Gain on sale of assets			$ 1,600,000