CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Current assets
Cash and cash equivalents	$ 1,936	$ 7,512
Accounts receivable, net of allowance for doubtful accounts	71,383	72,432
Derivative assets	14,836	18,987
Income taxes receivable	31,164	31,465
Other current assets	9,227	14,950
Total current assets	128,546	145,346
Property and equipment, net (successful efforts method)	1,809,291	1,777,575
Derivative assets	1,167
Other assets	19,699	20,132
Total assets	1,958,703	1,943,053
Current liabilities
Accounts payable and accrued liabilities	103,773	94,504
Derivative liabilities	7,262	3,549
Deferred income taxes	3,808	3,808
Current portion of long-term debt	4,791	4,746
Total current liabilities	119,634	106,607
Other liabilities	16,073	15,887
Derivative liabilities	8,437	6,850
Deferred income taxes	268,250	274,839
Long-term debt	712,848	692,561
Commitments and contingencies (Note 10)
Shareholders' equity:
Preferred stock of $100 par value - 100,000 shares authorized; none issued
Common stock of $0.01 par value - 128,000,000 shares authorized; shares issued of 45,827,010 and 45,714,191 as of March 31, 2012 and December 31, 2011, respectively	271	270
Paid-in capital	691,745	690,131
Retained earnings	142,757	157,242
Deferred compensation obligation	3,660	3,620
Accumulated other comprehensive loss	(1,061)	(1,084)
Treasury stock - 232,708 and 223,886 shares of common stock, at cost, as of March 31, 2012 and December 31, 2011, respectively	(3,911)	(3,870)
Total shareholders' equity	833,461	846,309
Total liabilities and shareholders' equity	$ 1,958,703	$ 1,943,053