Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Common Class A	Dec. 31, 2011 Common Class A	Dec. 31, 2012 Common Class B	Dec. 31, 2011 Common Class B
Current assets:
Cash and cash equivalents	$ 312	$ 298
Short-term investments	125	65
Accounts receivable	122,159	115,952
Deferred income taxes	703	13,779
Derivative instruments	14,661	6,117
Assets held for sale	0	14,622
Prepaid expenses and other	19,065	16,801
Total current assets	157,025	167,634
Oil and natural gas properties (successful efforts basis), buildings and equipment, net	3,128,502	2,531,393
Derivative instruments	10,891	7,027
Other assets	28,984	28,898
TOTAL ASSETS	3,325,402	2,734,952
Current liabilities:
Accounts payable	175,893	126,489
Revenue and royalties payable	57,021	49,253
Accrued liabilities	51,151	39,829
Derivative instruments	1,111	20,365
Deferred income taxes	1,456	0
Total current liabilities	286,632	235,936
Long-term liabilities:
Deferred income taxes	255,471	185,450
Senior secured revolving credit facility	562,900	531,500
8.25% Senior subordinated notes due 2016	0	200,000
Asset retirement obligations	82,316	59,256
Derivative instruments	1,239	15,505
Other long-term liabilities	19,136	17,884
Total long-term liabilities	2,023,979	1,658,287
Commitments and contingencies (Note 10)
Shareholders' equity:
Preferred stock, $0.01 par value, 2,000,000 shares authorized; no shares outstanding	0	0
Capital stock, $0.01 par value:
Common Stock			524	521	18	18
Capital in excess of par value	364,710	350,158
Accumulated other comprehensive loss	0	(5,517)
Retained earnings	649,539	495,549
Total shareholders' equity	1,014,791	840,729
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	$ 3,325,402	$ 2,734,952