Acquisitions and Divestitures (Details) (USD $)	9 Months Ended		0 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Jan. 31, 2012 Nevada Assets	Sep. 12, 2012 Brundage Canyon Acquisition [Member] acre	Apr. 13, 2012 2012 [Member] Wolfberry Acquisition acre	May 25, 2011 2011 [Member] Wolfberry Acquisition acre
Acquisitions
Interests acquired in oil and natural gas properties (in net acres)				14,000	2,000	6,000
Purchase price paid, net of customary post-closing adjustments	$ 75,706,000	$ 155,443,000		$ 39,600,000	$ 14,900,000	$ 128,400,000
Divestitures
Proceeds from sale of assets	17,294,000	0	15,600,000
Gain on sale of assets			$ 1,600,000