Decommissioning Liabilities (Details) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Feb. 29, 2012	Dec. 31, 2011
Summary of the activity for the Company's decommissioning liabilities
Decommissioning liabilities, December 31, 2011 and 2010, respectively	$ 123,176,000	$ 117,716,000
Liabilities acquired and incurred	3,573,000
Liabilities settled	(2,661,000)
Accretion	1,741,000	1,668,000
Total decommissioning liabilities, March 31, 2012 and 2011, respectively	125,829,000	119,384,000
Less: current portion of decommissioning liabilities at March 31, 2012 and 2011, respectively	15,678,000	17,063,000		14,956,000
Long-term decommissioning liabilities, March 31, 2012 and 2011, respectively	110,151,000	102,321,000		108,220,000
Decommissioning Liabilities (Textual) [Abstract]
Decommissioning liabilities			$ 3,600,000