Business Combinations (Narratives) (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended	7 Months Ended	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	May 31, 2012 [AlbaFieldMember]	Dec. 31, 2012 [AlbaFieldMember]	Dec. 14, 2012 [MaccullochFieldMember]
Business Acquisition [Line Items]
Business Acquisition, Cost of Acquired Entity, Purchase Price												$ 255,400,000
Business Combination, Step Acquisition, Equity Interest in Acquiree, Percentage												23.43%
Business Acquisition, Cost of Acquired Entity, Cash Paid												229,577,000
Proceeds from Notes Payable												205,000,000
Line of Credit Facility, Amount Outstanding												24,000,000
Percentage Of Assets Remaining To Be Acquired												25.68%
Total Deposit With Sellers Of Property														10,000,000
Acquisition Field Revenue	97,615,000	83,275,000	23,003,000	15,166,000	16,632,000	10,302,000	19,053,000	14,104,000	219,058,000	60,091,000	71,675,000		119,700,000
Acquisition income from operations	$ 37,758,000	$ 19,101,000	$ (18,356,000)	$ (18,701,000)	$ (34,168,000)	$ (32,222,000)	$ 749,000	$ (1,973,000)	$ 19,801,000	$ (67,614,000)	$ 1,327,000		$ 13,700,000