Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 974	$ 835
Accounts receivable, net of allowance for doubtful accounts of $5,174 and $5,199 at June 30, 2016 and December 31, 2015, respectively	67,506	79,941
Materials and supplies	3,324	3,565
Current derivative asset (Note 10)	0	10,186
Current income tax receivable	2,033	21,002
Current deferred tax asset	8,598	14,206
Assets held for sale	0	615
Prepaid expenses and other	6,859	9,908
Total current assets	89,294	140,258
Oil and natural gas properties on the full cost method:
Proved properties	5,420,972	5,401,618
Unproved properties not being amortized	321,191	337,099
Drilling equipment	1,567,765	1,567,560
Gas gathering and processing equipment	697,573	689,063
Saltwater disposal systems	60,527	60,316
Corporate land and building	56,149	49,890
Transportation equipment	34,055	40,072
Other	45,777	45,489
Property, plant, and equipment, gross	8,204,009	8,191,107
Less accumulated depreciation, depletion, amortization, and impairment	5,818,163	5,609,980
Net property and equipment	2,385,846	2,581,127
Goodwill	62,808	62,808
Non-current derivative asset (Note 10)	0	968
Other assets	14,148	14,681
Total assets	2,552,096	2,799,842
Current liabilities:
Accounts payable	72,744	87,413
Accrued liabilities (Note 5)	46,368	46,918
Current derivative liability (Note 10)	9,646	0
Current portion of other long-term liabilities (Note 6)	17,999	16,560
Total current liabilities	146,757	150,891
Long-term debt less debt issuance costs (Note 6)	875,051	918,995
Non-current derivative liability (Note 10)	3,420	285
Other long-term liabilities (Note 6)	103,926	140,341
Deferred income taxes	211,721	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, 51,504,959 and 50,413,101 shares issued as of June 30, 2016 and December 31, 2015, respectively	10,016	9,831
Capital in excess of par value	497,312	486,571
Retained earnings	703,893	817,178
Total shareholders' equity	1,211,221	1,313,580
Total liabilities and shareholders' equity	$ 2,552,096	$ 2,799,842