Acquisitions and Divestitures (Details) (USD $)	3 Months Ended		0 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Jan. 31, 2012 Nevada Assets	Sep. 12, 2012 Brundage Canyon Acquisition acre	Apr. 13, 2012 Wolfberry Acquisition acre
Business Acquisition
Interests acquired in oil and natural gas properties (in net acres)				14,000	2,000
Purchase price paid, net of customary post-closing adjustments	$ 2,897,000	$ 8,529,000		$ 39,600,000	$ 14,900,000
Divestitures
Proceeds from sale of assets	480,000	15,700,000	15,600,000
Gain on sale of assets			$ 1,600,000