Condensed Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Current assets:
Cash and cash equivalents	$ 1,741	$ 974
Accounts receivable, net of allowance for doubtful accounts of $5,342 and $5,343 at September 30, 2013 and at December 31, 2012, respectively	141,817	146,046
Materials and supplies	10,330	8,563
Current derivative asset (Note 10)	4,514	16,552
Current income tax receivable	1,389	901
Current deferred tax asset	9,371	8,765
Prepaid expenses and other	12,413	13,843
Total current assets	181,575	195,644
Oil and natural gas properties on the full cost method:
Proved properties	4,061,108	3,822,381
Undeveloped leasehold not being amortized	589,227	521,659
Drilling equipment	1,484,928	1,478,645
Gas gathering and processing equipment	538,258	461,629
Transportation equipment	39,286	37,728
Other	74,802	62,840
Property, plant and equipment, gross, total	6,787,609	6,384,882
Less accumulated depreciation, depletion, amortization, and impairment	3,133,717	2,907,660
Net property and equipment	3,653,892	3,477,222
Debt issuance cost	12,241	13,432
Goodwill	62,808	62,808
Other intangible assets, net	0	680
Non-current derivative asset (Note 10)	1,133	0
Other assets	13,046	11,334
Total assets	3,924,695	3,761,120
Current liabilities:
Accounts payable	132,633	138,811
Accrued liabilities (Note 5)	78,557	54,098
Current portion of derivative liabilities (Note 10)	6,480	1,948
Current portion of other long-term liabilities (Note 6)	11,985	12,282
Total current liabilities	229,655	207,139
Long-term debt (Note 6)	645,584	716,359
Non-current derivative liabilities (Note 10)	938	562
Other long-term liabilities (Note 6)	158,161	166,983
Deferred income taxes	773,412	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, 49,091,928 and 48,581,948 shares issued, respectively	9,655	9,594
Capital in excess of par value	441,291	423,603
Accumulated other comprehensive income (loss) (Note 12)	(963)	7,587
Retained earnings	1,666,962	1,533,517
Total shareholders' equity	2,116,945	1,974,301
Total liabilities and shareholders' equity	$ 3,924,695	$ 3,761,120