CONDENSED CONSOLIDATED BALANCE SHEETS (USD $) In Thousands	Jun. 30, 2011	Dec. 31, 2010
Current assets
Cash and cash equivalents	$ 30,681	$ 120,911
Accounts receivable, net of allowance for doubtful accounts	67,779	72,378
Derivative assets	14,440	16,818
Other current assets	3,904	4,233
Total current assets	116,804	214,340
Property and equipment, net (successful efforts method)	1,728,121	1,705,584
Derivative assets	2,547	3,889
Other assets	22,158	20,787
Total assets	1,869,630	1,944,600
Current liabilities
Accounts payable and accrued liabilities	89,324	99,661
Derivative liabilities	115	388
Deferred income taxes	3,113	4,318
Income taxes payable	2,820	2,627
Total current liabilities	95,372	106,994
Other liabilities	18,578	19,958
Deferred income taxes	276,405	330,836
Long-term debt	597,668	506,536
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 45,688,179 and 45,556,854 as of June 30, 2011and December 31, 2010, respectively	269	267
Paid-in capital	685,559	680,981
Retained earnings	197,059	300,473
Deferred compensation obligation	3,235	2,743
Accumulated other comprehensive loss	(870)	(938)
Treasury stock - 162,209 and 125,357 shares of common stock, at cost, as of June 30, 2011 and December 31, 2010, respectively	(3,645)	(3,250)
Total shareholders' equity	881,607	980,276
Total liabilities and shareholders' equity	$ 1,869,630	$ 1,944,600