Condensed Consolidated Balance Sheets (Unaudited) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 752,000	$ 701,000
Accounts receivable, net of allowance for doubtful accounts of $2,450 at both March 31, 2018 and December 31, 2017, respectively	98,506,000	111,512,000
Materials and supplies	455,000	505,000
Current derivative asset (Note 10)	537,000	721,000
Current income tax receivable	61,000	0
Prepaid expenses and other	7,724,000	6,233,000
Total current assets	108,035,000	119,672,000
Oil and natural gas properties on the full cost method:
Proved properties	5,762,069,000	5,712,813,000
Unproved properties not being amortized	305,621,000	296,764,000
Drilling equipment	1,601,777,000	1,593,611,000
Gas gathering and processing equipment	731,006,000	726,236,000
Saltwater disposal systems	63,124,000	62,618,000
Corporate land and building	59,080,000	59,080,000
Transportation equipment	29,908,000	29,631,000
Other	56,142,000	53,439,000
Property, plant, and equipment, gross	8,608,727,000	8,534,192,000
Less accumulated depreciation, depletion, amortization, and impairment	6,207,449,000	6,151,450,000
Net property and equipment	2,401,278,000	2,382,742,000
Goodwill	62,808,000	62,808,000
Other assets	27,470,000	16,230,000
Total assets	2,599,591,000	2,581,452,000
Current liabilities:
Accounts payable	131,064,000	112,648,000
Accrued liabilities (Note 5)	52,964,000	48,523,000
Current derivative liability (Note 10)	12,104,000	7,763,000
Current portion of other long-term liabilities (Note 6)	14,587,000	13,002,000
Total current liabilities	210,719,000	181,936,000
Long-term debt less debt issuance costs (Note 6)	790,522,000	820,276,000
Non-current derivative liability (Note 10)	164,000	0
Other long-term liabilities (Note 6)	104,286,000	100,203,000
Deferred income taxes	136,600,000	133,477,000
Commitments and contingencies (Note 12)	0	0
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, 54,046,361 and 52,880,134 shares issued as of March 31, 2018 and December 31, 2017, respectively	10,403,000	10,280,000
Capital in excess of par value	541,004,000	535,815,000
Accumulated other comprehensive income (Note 13)	(100,000)	63,000
Retained earnings	805,993,000	799,402,000
Total shareholders' equity	1,357,300,000	1,345,560,000
Total liabilities and shareholders' equity	$ 2,599,591,000	$ 2,581,452,000