Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Current Assets
Cash and cash equivalents	$ 498	$ 386,093
Accounts receivable, net	104,359	73,322
Inventories, net	18,263	14,222
Derivative instruments	39,063	50
Income tax receivable	301	27,153
Prepayments and other	4,410	5,071
Total current assets	166,894	505,911
Oil and natural gas properties, successful efforts method
Proved properties	8,024,501	7,543,464
Unproved properties	430,079	196,888
Less accumulated depreciation, depletion and amortization	(3,940,837)	(3,723,669)
Oil and natural gas properties, net	4,513,743	4,016,683
Other property and equipment, net	45,241	44,869
Total property, plant and equipment, net	4,558,984	4,061,552
Other postretirement assets	3,595	3,619
Noncurrent derivative instruments	9,534	0
Other assets	7,725	8,741
TOTAL ASSETS	4,746,732	4,579,823
Current Liabilities
Long-term debt due within one year	17,000	24,000
Accounts payable	65,770	65,031
Accrued taxes	12,734	7,252
Accrued wages and benefits	15,709	25,089
Accrued capital costs	95,509	79,988
Revenue and royalty payable	48,332	51,217
Derivative instruments	481	65,467
Other	17,778	20,160
Total current liabilities	273,313	338,204
Long-term debt	659,158	527,443
Asset retirement obligations	84,867	81,544
Deferred income taxes	532,605	495,888
Noncurrent derivative instruments	502	3,006
Other long-term liabilities	8,545	13,136
Total liabilities	1,558,990	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; 100,311,561 shares and 100,138,797 shares issued at June 30, 2017 and December 31, 2016, respectively	1,003	1,001
Premium on capital stock	1,380,310	1,372,569
Retained earnings	1,941,218	1,878,503
Accumulated other comprehensive income, net of tax
Postretirement plans	1,267	1,405
Deferred compensation plan	2,727	2,261
Treasury stock, at cost; 3,192,058 shares and 3,125,715 shares at June 30, 2017 and December 31, 2016, respectively	(138,783)	(135,137)
Total shareholders’ equity	3,187,742	3,120,602
TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY	$ 4,746,732	$ 4,579,823