Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 1,153	$ 974
Accounts receivable, net of allowance for doubtful accounts of $5,343 both at March 31, 2013 and at December 31, 2012	151,770	146,046
Materials and supplies	9,203	8,563
Current derivative asset (Note 9)	3,217	16,552
Current income tax receivable	0	901
Current deferred tax asset	11,671	8,765
Prepaid expenses and other	12,561	13,843
Total current assets	189,575	195,644
Oil and natural gas properties on the full cost method:
Proved properties	3,907,576	3,822,381
Undeveloped leasehold not being amortized	538,224	521,659
Drilling equipment	1,484,701	1,478,645
Gas gathering and processing equipment	484,008	461,629
Transportation equipment	39,081	37,728
Other	66,397	62,840
Property, plant and equipment, gross, total	6,519,987	6,384,882
Less accumulated depreciation, depletion, amortization, and impairment	2,982,463	2,907,660
Net property and equipment	3,537,524	3,477,222
Debt issuance cost	13,035	13,432
Goodwill	62,808	62,808
Other intangible assets, net	425	680
Other assets	11,473	11,334
Total assets	3,814,840	3,761,120
Current liabilities:
Accounts payable	131,829	138,811
Accrued liabilities (Note 4)	53,324	54,098
Income taxes payable	989	0
Current portion of derivative liabilities (Note 9)	13,828	1,948
Current portion of other long-term liabilities (Note 5)	12,484	12,282
Total current liabilities	212,454	207,139
Long-term debt (Note 5)	715,365	716,359
Non-current derivative liabilities (Note 9)	1,081	562
Other long-term liabilities (Note 5)	157,429	166,983
Deferred income taxes	718,498	695,776
Shareholders' equity:
Preferred stock, $1.00 par value, 5,000,000 shares authorized, none issued	0	0
Common stock, $.20 par value, 175,000,000 shares authorized, 49,091,943 and 48,581,948 shares issued, respectively	9,637	9,594
Capital in excess of par value	430,491	423,603
Accumulated other comprehensive income (loss) (Note 11)	(3,838)	7,587
Retained earnings	1,573,723	1,533,517
Total shareholders' equity	2,010,013	1,974,301
Total liabilities and shareholders' equity	$ 3,814,840	$ 3,761,120