Acquisitions and Divestures (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended			0 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Nevada Assets	May 25, 2011 Wolfberry Acquisition acre
Acquisitions
Interests acquired in producing properties (in net acres)				6,000
Purchase price paid, net of customary post-closing adjustments	$ 8,529	$ 2,413		$ 128,400
Divestures
Proceeds from sale of assets	15,700	0	15,600
Gain on sale of assets	$ 1,763	$ 0	$ 1,700