Condensed Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 105	$ 312
Restricted short-term investments	125	125
Accounts receivable	131,632	122,159
Deferred income taxes	6,093	703
Derivative instruments	7,622	14,661
Prepaid expenses and other	22,205	19,065
Total current assets	167,782	157,025
Oil and natural gas properties (successful efforts basis), buildings and equipment, net	3,177,892	3,128,502
Derivative instruments	17,491	10,891
Other assets	27,468	28,984
TOTAL ASSETS	3,390,633	3,325,402
Current liabilities:
Accounts payable	108,713	175,893
Revenue and royalties payable	31,564	57,021
Accrued liabilities	47,183	51,151
Derivative instruments	5,057	1,111
Deferred income taxes	0	1,456
Total current liabilities	192,517	286,632
Long-term liabilities:
Deferred income taxes	281,925	255,471
Senior secured revolving credit facility	653,600	562,900
Asset Retirement Obligations, Noncurrent	90,237	82,316
Derivative instruments	0	1,239
Other long-term liabilities	22,241	19,136
Total long-term liabilities	2,151,310	2,023,979
Shareholders' equity:
Preferred stock, $0.01 par value, 2,000,000 shares authorized; no shares outstanding	0	0
Capital in excess of par value	368,688	364,710
Retained earnings	677,573	649,539
Total shareholders' equity	1,046,806	1,014,791
TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY	3,390,633	3,325,402
Class A
Capital stock, $0.01 par value:
Common Stock	527	524
Class B
Capital stock, $0.01 par value:
Common Stock	18	18
10.25% Senior notes due 2014, net of unamortized discount
Long-term liabilities:
Senior notes	203,307	202,917
6.75% Senior notes due 2020
Long-term liabilities:
Senior notes	300,000	300,000
6.375% Senior notes due 2022
Long-term liabilities:
Senior notes	$ 600,000	$ 600,000