CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 439	$ 386,093
Accounts receivable, net	158,787	73,322
Inventories, net	13,177	14,222
Derivative instruments	0	50
Income tax receivable	6,905	27,153
Prepayments and other	12,085	5,071
Total current assets	191,393	505,911
Oil and natural gas properties, successful efforts method
Proved properties	8,466,708	7,543,464
Unproved properties	453,028	196,888
Less accumulated depreciation, depletion and amortization	(4,200,797)	(3,723,669)
Oil and natural gas properties, net	4,718,939	4,016,683
Other property and equipment, net	44,581	44,869
Total property, plant and equipment, net	4,763,520	4,061,552
Other postretirement assets	2,646	3,619
Noncurrent income tax receivable, net	70,716	0
Other assets	5,620	8,741
TOTAL ASSETS	5,033,895	4,579,823
Current Liabilities
Long-term debt due within one year	0	24,000
Accounts payable	75,167	65,031
Accrued taxes	2,631	7,252
Accrued wages and benefits	26,170	25,089
Accrued capital costs	74,909	79,988
Revenue and royalty payable	54,072	51,217
Derivative instruments	71,379	65,467
Other	17,916	20,160
Total current liabilities	322,244	338,204
Long-term debt	782,861	527,443
Asset retirement obligations	88,378	81,544
Noncurrent derivative instruments	8,886	3,006
Deferred income taxes	387,807	495,888
Other long-term liabilities	5,262	13,136
Total liabilities	1,595,438	1,459,221
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; 100,327,433 shares issued at December 31, 2017 and 100,138,797 shares issued at December 31, 2016	1,003	1,001
Premium on capital stock	1,388,082	1,372,569
Retained earnings	2,185,161	1,878,503
Accumulated other comprehensive income, net of tax
Postretirement plans	380	1,405
Deferred compensation plan	2,681	2,261
Treasury stock, at cost; 3,192,252 shares and 3,125,715 shares at December 31, 2017 and 2016, respectively	(138,850)	(135,137)
Total shareholders’ equity	3,438,457	3,120,602
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 5,033,895	$ 4,579,823