Asset Retirement Obligations (Tables)

3 Months Ended

Mar. 31, 2018

Asset Retirement Obligation Disclosure [Abstract]

Summary of Asset Retirement Obligations

The following table summarizes the changes in the reserve for future restoration and reclamation costs on the balance sheet:

	March 31,			December 31,
	2018			2017
(thousands of dollars)
Balance, beginning of period	$	5,731		$	4,789
Liabilities settled		(142	)		(97	)
Accretion expense		134			1,039
Balance, end of period		5,723			5,731
Less: Current portion		(936	)		(1,078	)
Non-current portion	$	4,787		$	4,653