Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 88,658	$ 386,093
Accounts receivable, net	90,100	73,322
Inventories, net	15,365	14,222
Derivative instruments	7,594	50
Income tax receivable	26,246	27,153
Prepayments and other	5,024	5,071
Total current assets	232,987	505,911
Oil and natural gas properties, successful efforts method
Proved properties	7,767,171	7,543,464
Unproved properties	354,940	196,888
Less accumulated depreciation, depletion and amortization	(3,823,200)	(3,723,669)
Oil and natural gas properties, net	4,298,911	4,016,683
Other property and equipment, net	45,606	44,869
Total property, plant and equipment, net	4,344,517	4,061,552
Other postretirement assets	3,607	3,619
Noncurrent derivative instruments	9,293	0
Other assets	8,311	8,741
TOTAL ASSETS	4,598,715	4,579,823
Current Liabilities
Long-term debt due within one year	17,000	24,000
Accounts payable	79,644	65,031
Accrued taxes	10,153	7,252
Accrued wages and benefits	14,047	25,089
Accrued capital costs	120,825	79,988
Revenue and royalty payable	44,314	51,217
Derivative instruments	8,324	65,467
Other	14,368	20,160
Total current liabilities	308,675	338,204
Long-term debt	527,557	527,443
Asset retirement obligations	83,256	81,544
Deferred income taxes	516,295	495,888
Noncurrent derivative instruments	0	3,006
Other long-term liabilities	8,381	13,136
Total liabilities	1,444,164	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; 100,309,842 shares and 100,138,797 shares issued at March 31, 2017 and December 31, 2016, respectively	1,003	1,001
Premium on capital stock	1,376,517	1,372,569
Retained earnings	1,911,737	1,878,503
Accumulated other comprehensive income, net of tax
Postretirement plans	1,336	1,405
Deferred compensation plan	2,687	2,261
Treasury stock, at cost; 3,191,149 shares and 3,125,715 shares at March 31, 2017 and December 31, 2016, respectively	(138,729)	(135,137)
Total shareholders’ equity	3,154,551	3,120,602
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 4,598,715	$ 4,579,823