Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES
Net income (loss)	$ (17,662)	$ 21,647
Adjustments to reconcile net income (loss) to net cash provided by operating activities
Depreciation, depletion and amortization	98,186	86,929
Exploration expense	20,827	14,206
Stock-based compensation	6,131	6,857
Accretion of asset retirement obligations	486	395
(Gain) loss on derivative instruments	24,055	(41,385)
Net cash receipts (payments) on settled derivatives	(7,724)	(5,048)
(Gain) loss on sale of assets	(1,814)	(12)
Amortization of deferred financing costs	1,677	1,553
Amortization of debt discount	995	992
Changes in operating assets and liabilities:
Accounts receivable	(48,601)	4,357
Other assets	(2,144)	56
Accounts payable and accrued liabilities	18,989	(3,344)
Net cash provided by operating activities	93,401	87,203
CASH FLOWS FROM INVESTING ACTIVITIES
Capital expenditures for oil and gas properties	(210,612)	(254,353)
Capital expenditures for other property and equipment	(892)	(1,901)
Proceeds from sale of assets	10,348	551
Net cash used in investing activities	(201,156)	(255,703)
CASH FLOWS FROM FINANCING ACTIVITIES
Debt issuance costs	(108)	(1,657)
Repayments of long-term debt	(381)	(198)
Proceeds from credit facility	99,000
Equity issuance costs	(307)	(44)
Employee tax withholding for settlement of equity compensation awards	(1,261)	(2,035)
Net cash provided by (used in) financing activities	96,943	(3,934)
Net increase (decrease) in cash and cash equivalents	(10,812)	(172,434)
Cash and cash equivalents at beginning of period	17,224	201,229
Cash and cash equivalents at end of period	6,412	28,795
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION
Cash paid for interest	49,280	46,638
SUPPLEMENTAL DISCLOSURE OF NON-CASH ACTIVITIES
Asset retirement obligations incurred, including changes in estimate	388	565
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	3,988	$ 27,125
Asset acquisition through stock issuance	$ 90,020