Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Activities
Net loss	$ (20,042)	$ (730,096)
Adjustments to reconcile net loss to net cash provided by operating activities:
Depletion, depreciation and accretion	98,300	131,118
Goodwill impairment (Note 5)	0	102,581
Asset impairment (Note 5)	0	507,093
Deferred tax expense (recovery)	26,809	(62,796)
Stock-based compensation expense (recovery) (Note 7)	6,597	(707)
Amortization of debt issuance costs (Note 6)	2,682	2,774
Unrealized foreign exchange loss	16,945	22,335
Derivative instruments loss (gain) (Note 12)	47,540	(9,417)
Cash settlements on derivatives instruments	(45,041)	9,970
Other financial instruments (gain) loss (Note 12)	(12,425)	61,286
Other non-cash loss	0	2,026
Cash settlement of asset retirement obligation	(483)	(199)
Non-cash lease expenses	1,222	1,494
Lease payments	(1,239)	(1,404)
Net change in assets and liabilities from operating activities (Note 13)	17,956	23,288
Net cash provided by operating activities	138,821	59,346
Investing Activities
Additions to property, plant and equipment	(109,650)	(56,378)
Proceeds on disposition of investment, net of transaction costs (Note 12)	14,632	0
Changes in non-cash investing working capital (Note 13)	709	(69,549)
Net cash used in investing activities	(94,309)	(125,927)
Financing Activities
Proceeds from debt, net of issuance costs (Note 6)	(125)	88,382
Repayment of debt (Note 6)	(40,000)	(7,000)
Proceeds from exercise of stock options	19	0
Lease payments	(1,269)	(307)
Net cash (used in) provided by financing activities	(41,375)	81,075
Foreign exchange loss on cash, cash equivalents and restricted cash and cash equivalents	(528)	(754)
Net increase in cash, cash equivalents and restricted cash and cash equivalents	2,609	13,740
Cash, cash equivalents and restricted cash and cash equivalents, beginning of period (Note 13)	17,523	11,075
Cash, cash equivalents and restricted cash and cash equivalents, end of period (Note 13)	$ 20,132	$ 24,815