Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 1,188	$ 439
Accounts receivable, net	166,467	158,787
Inventories, net	29,255	13,177
Derivative instruments	35,377	0
Income tax receivable	6,904	6,905
Prepayments and other	6,086	12,085
Total current assets	245,277	191,393
Oil and natural gas properties, successful efforts method
Proved properties	9,031,307	8,466,708
Unproved properties	513,501	453,028
Less accumulated depreciation, depletion and amortization	(4,455,488)	(4,200,797)
Oil and natural gas properties, net	5,089,320	4,718,939
Other property and equipment, net	43,896	44,581
Total property, plant and equipment, net	5,133,216	4,763,520
Other postretirement assets	2,609	2,646
Noncurrent derivative instruments	258	0
Noncurrent income tax receivable, net	70,716	70,716
Other assets	9,936	5,620
TOTAL ASSETS	5,462,012	5,033,895
Current Liabilities
Accounts payable	74,568	75,167
Accrued taxes	12,287	2,631
Accrued wages and benefits	11,428	26,170
Accrued capital costs	165,873	74,909
Revenue and royalty payable	68,154	54,072
Derivative instruments	80,996	71,379
Other	18,708	17,916
Total current liabilities	432,014	322,244
Long-term debt	829,068	782,861
Asset retirement obligations	92,588	88,378
Noncurrent derivative instruments	31,035	8,886
Deferred income taxes	442,225	387,807
Other long-term liabilities	6,223	5,262
Total liabilities	1,833,153	1,595,438
Commitments and Contingencies
Shareholders’ Equity
Preferred stock, cumulative, $0.01 par value, 5,000,000 shares authorized	0	0
Common shareholders’ equity
Common stock, $0.01 par value; 150,000,000 shares authorized; 100,707,670 shares and 100,327,433 shares issued at June 30, 2018 and December 31, 2017, respectively	1,007	1,003
Premium on capital stock	1,398,320	1,388,082
Retained earnings	2,372,063	2,185,161
Accumulated other comprehensive income, net of tax
Postretirement plans	543	380
Deferred compensation plan	3,284	2,681
Treasury stock, at cost; 3,332,714 shares and 3,192,252 shares at June 30, 2018 and December 31, 2017, respectively	(146,358)	(138,850)
Total shareholders’ equity	3,628,859	3,438,457
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 5,462,012	$ 5,033,895