Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current Assets
Cash and cash equivalents	$ 600	$ 439
Accounts receivable, net	150,813	158,787
Inventories, net	19,586	13,177
Derivative instruments	4,984	0
Income tax receivable	6,899	6,905
Prepayments and other	9,773	12,085
Total current assets	192,655	191,393
Oil and natural gas properties, successful efforts method
Proved properties	8,706,155	8,466,708
Unproved properties	505,416	453,028
Less accumulated depreciation, depletion and amortization	(4,323,834)	(4,200,797)
Oil and natural gas properties, net	4,887,737	4,718,939
Other property and equipment, net	44,427	44,581
Total property, plant and equipment, net	4,932,164	4,763,520
Other postretirement assets	2,627	2,646
Noncurrent derivative instruments	3,261	0
Noncurrent income tax receivable, net	70,716	70,716
Other assets	4,341	5,620
TOTAL ASSETS	5,205,764	5,033,895
Current Liabilities
Accounts payable	104,430	75,167
Accrued taxes	6,411	2,631
Accrued wages and benefits	8,936	26,170
Accrued capital costs	111,887	74,909
Revenue and royalty payable	62,517	54,072
Derivative instruments	57,478	71,379
Other	12,239	17,916
Total current liabilities	363,898	322,244
Long-term debt	755,964	782,861
Asset retirement obligations	90,295	88,378
Noncurrent derivative instruments	11,563	8,886
Deferred income taxes	423,228	387,807
Other long-term liabilities	5,969	5,262
Total liabilities	1,650,917	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; 100,653,429 shares and 100,327,433 shares issued at March 31, 2018 and December 31, 2017, respectively	1,007	1,003
Premium on capital stock	1,392,109	1,388,082
Retained earnings	2,303,789	2,185,161
Accumulated other comprehensive income, net of tax
Postretirement plans	604	380
Deferred compensation plan	3,223	2,681
Treasury stock, at cost; 3,326,036 shares and 3,192,252 shares at March 31, 2018 and December 31, 2017, respectively	(145,885)	(138,850)
Total shareholders’ equity	3,554,847	3,438,457
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 5,205,764	$ 5,033,895