CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 578,908	$ 652,876
Accounts receivable:
Trade, net of allowance	69,324	42,287
Oil and gas sales, net of allowance	238,149	217,395
Gas gathering, processing, and marketing, net of allowance	11,657	14,888
Other	12	27
Oil and gas well equipment and supplies	37,487	33,342
Derivative instruments	6,381
Prepaid expenses	5,715	7,335
Other current assets	1,594	1,154
Total current assets	949,227	969,304
Oil and gas properties at cost, using the full cost method of accounting:
Proved properties	16,519,581	16,225,495
Unproved properties and properties under development, not being amortized	489,888	478,277
Gross oil and gas properties	17,009,469	16,703,772
Less - accumulated depreciation, depletion, amortization and impairment	(14,434,516)	(14,349,505)
Net oil and gas properties	2,574,953	2,354,267
Fixed assets, net of accumulated depreciation of $257,561 and $246,901, respectively	203,917	205,465
Goodwill	620,232	620,232
Derivative instruments	2,438
Deferred income taxes	10,424	55,835
Other assets, net	32,808	32,621
Total assets	4,393,999	4,237,724
Accounts payable:
Trade	62,035	49,163
Gas gathering, processing, and marketing	24,147	25,323
Accrued liabilities:
Exploration and development	73,420	82,320
Taxes other than income	15,554	18,766
Other	179,952	177,695
Derivative instruments	10,838	49,370
Revenue payable	141,376	119,715
Total current liabilities	507,322	522,352
Long-term debt:
Principal	1,500,000	1,500,000
Less - unamortized debt issuance costs	(11,500)	(12,061)
Long-term debt, net	1,488,500	1,487,939
Asset retirement obligation	144,523	140,770
Derivative instruments		2,570
Other liabilities	42,705	41,104
Total liabilities	2,183,050	2,194,735
Commitments and contingencies (Note 10)
Stockholders' equity:
Preferred stock, $0.01 par value, 15,000,000 shares authorized, no shares issued
Common stock, $0.01 par value, 200,000,000 shares authorized, 95,116,764 and 95,123,525 shares issued, respectively	951	951
Additional paid-in capital	2,771,296	2,763,452
Retained earnings (Accumulated deficit)	(562,645)	(722,359)
Accumulated other comprehensive income	1,347	945
Total stockholders' equity	2,210,949	2,042,989
Total liabilities and stockholders' equity	$ 4,393,999	$ 4,237,724