Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ (2,626)	$ 26,847
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities
Depreciation, depletion and amortization	31,156	26,189
Exploration expense	6,790	4,988
Stock-based compensation	1,981	2,081
Accretion of asset retirement obligations	155	124
(Gain) loss on derivative instruments	4,215	(25,097)
Net cash receipts (payments) on settled derivatives	141	(3,989)
(Gain) loss on sale of assets	(267)	(5)
Amortization of deferred financing costs	554	502
Amortization of debt discount	332	330
Changes in operating assets and liabilities:
Accounts receivable	(35,499)	10,478
Other assets	(459)	943
Accounts payable and accrued liabilities	(3,179)	(14,992)
Net cash provided by operating activities	3,294	28,399
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures for oil and gas properties	(66,441)	(66,005)
Capital expenditures for other property and equipment	(155)	(178)
Proceeds from sale of assets	4,099	24
Net cash used in investing activities	(62,497)	(66,159)
CASH FLOWS FROM FINANCING ACTIVITIES
Debt issuance costs	(48)	(1,231)
Repayments of long-term debt	(92)	(74)
Proceeds from credit facility	65,000
Equity issuance costs	(145)
Employee tax withholding for settlement of equity compensation awards	(935)	(1,706)
Net cash provided by (used in) financing activities	63,780	(3,011)
Net increase (decrease) in cash and cash equivalents	4,577	(40,771)
Cash and cash equivalents at beginning of period	17,224	201,229
Cash and cash equivalents at end of period	21,801	160,458
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest	23,638	23,066
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES
Asset retirement obligations incurred, including changes in estimate	85	124
Additions of other property through debt financing	174
Additions to oil and natural gas properties - changes in accounts payable, accrued liabilities, and accrued capital expenditures	8,864	$ 13,126
Asset acquisition through stock issuance	$ 90,020