Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($)	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ 21,647,000	$ (144,646,000)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Depreciation, depletion and amortization	86,929,000	64,287,000
Exploration expense	14,206,000	28,952,000
Stock-based compensation	6,857,000	5,464,000
Impairment of proved oil and gas properties		17,665,000
Accretion of asset retirement obligations	395,000	275,000
(Gain) loss on derivative instruments	(41,385,000)	8,407,000
Net cash receipts (payments) on settled derivatives	(5,048,000)	35,870,000
(Gain) loss on sale of assets	(12,000)	(944,000)
(Gain) loss on early extinguishment of debt		(14,489,000)
Deferred income taxes	0	540,000
Amortization of deferred financing costs	1,553,000	1,457,000
Amortization of debt discount	992,000	1,033,000
Changes in operating assets and liabilities:
Accounts receivable	4,357,000	(1,797,000)
Other assets	56,000	(1,902,000)
Accounts payable and accrued liabilities	(3,344,000)	(28,659,000)
Net cash provided by (used in) operating activities	87,203,000	(28,487,000)
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures for oil and gas properties	(254,353,000)	(92,204,000)
Capital expenditures for other property and equipment	(1,901,000)	(852,000)
Proceeds from sale of assets	551,000	14,887,000
Net cash used in investing activities	(255,703,000)	(78,169,000)
CASH FLOWS FROM FINANCING ACTIVITIES
Debt issuance costs	(1,657,000)	40,000
Repayments of long-term debt	(198,000)	(23,936,000)
Proceeds from issuance of common stock		124,361,000
Equity issuance costs	(44,000)	(484,000)
Employee tax withholding for settlement of equity compensation awards	(2,035,000)	(61,000)
Net cash provided by (used in) financing activities	(3,934,000)	99,920,000
Net decrease in cash and cash equivalents	(172,434,000)	(6,736,000)
Cash and cash equivalents at beginning of period	201,229,000	184,405,000
Cash and cash equivalents at end of period	28,795,000	177,669,000
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest	46,638,000	48,101,000
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES
Asset retirement obligations incurred, including changes in estimate	565,000	923,000
Additions to oil and natural gas properties - changes in accounts payable, accrued liabilities, and accrued capital expenditures	$ 27,125,000	$ 26,055,000