Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 739	$ 835
Accounts receivable, net of allowance for doubtful accounts of $5,199 at both March 31, 2016 and December 31, 2015, respectively	68,424	79,941
Materials and supplies	3,303	3,565
Current derivative asset (Note 10)	13,901	10,186
Current income tax receivable	20,652	21,002
Current deferred tax asset	8,598	14,206
Assets held for sale	225	615
Prepaid expenses and other	8,250	9,908
Total current assets	124,092	140,258
Oil and natural gas properties on the full cost method:
Proved properties	5,387,103	5,401,618
Unproved properties not being amortized	330,274	337,099
Drilling equipment	1,569,740	1,567,560
Gas gathering and processing equipment	691,759	689,063
Saltwater disposal systems	60,459	60,316
Corporate land and building	55,077	49,890
Transportation equipment	38,659	40,072
Other	45,845	45,489
Property, plant, and equipment, gross	8,178,916	8,191,107
Less accumulated depreciation, depletion, amortization, and impairment	5,700,840	5,609,980
Net property and equipment	2,478,076	2,581,127
Goodwill	62,808	62,808
Non-current derivative asset (Note 10)	942	968
Other assets	15,170	14,681
Total assets	2,681,088	2,799,842
Current liabilities:
Accounts payable	67,504	87,413
Accrued liabilities (Note 5)	52,854	46,918
Current portion of other long-term liabilities (Note 6)	19,053	16,560
Total current liabilities	139,411	150,891
Long-term debt less debt issuance costs (Note 6)	898,722	918,995
Non-current derivative liability (Note 10)	185	285
Other long-term liabilities (Note 6)	106,930	140,341
Deferred income taxes	254,800	275,750
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, 51,440,785 and 50,413,101 shares issued as of March 31, 2016 and December 31, 2015, respectively	10,012	9,831
Capital in excess of par value	494,999	486,571
Retained earnings	776,029	817,178
Total shareholders' equity	1,281,040	1,313,580
Total liabilities and shareholders' equity	$ 2,681,088	$ 2,799,842