ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH

The following table summarizes the Company’s asset retirement obligations:



	June 30, 2018			December 31, 2017
Asset retirement obligation, beginning of period	$	18,280		$	17,033
Revision of estimate	—			249
Accretion of liabilities	917			1,733
Settlements	(151		)	(735		)
Asset retirement obligation, end of period	$	19,046		$	18,280
Asset retirement obligation:
Current	$	32		$	32
Non-current	19,014			18,248
Asset retirement obligation, end of period	$	19,046		$	18,280

The asset retirement obligations of the Company are subject to legal and regulatory requirements. Estimates of the costs of reclamation are reviewed periodically by the Company and the applicable regulatory authorities. The above provision represents the Company’s best estimate of the present value of future reclamation costs, discounted using credit adjusted risk-free interest rates ranging from 9.5% to 11.5% and an inflation rate of 2.0%. The total undiscounted decommissioning liability at June 30, 2018 is $43.31 million (December 31, 2017 - $43.46 million).

The following table summarizes the Company’s restricted cash:



	June 30, 2018			December 31, 2017
Restricted cash, beginning of period	$	22,127		$	23,175
Additional collateral posted	102			13,609
Refunds of collateral	(635		)	(14,657		)
Restricted cash, end of period	$	21,594		$	22,127

The Company has cash, cash equivalents and fixed income securities as collateral for various bonds posted in favor of the applicable state regulatory agencies in Arizona, Colorado, New Mexico, Texas, Utah and Wyoming, and the U.S. Bureau of Land Management and U.S. Forest Service for estimated reclamation costs associated with the White Mesa Mill, Nichols Ranch, Alta Mesa and other mining properties. Cash equivalents are short-term highly liquid investments with original maturities of three months or less. The restricted cash will be released when the Company has reclaimed a mineral property or restructured the surety and collateral arrangements. See Note 12 for a discussion of the Company’s surety bond commitments.

Cash, cash equivalents and restricted cash are included in the following accounts at June 30, 2018 and December 31, 2017:



	June 30, 2018		December 31, 2017
Cash and cash equivalents	$	43,239	$	18,574
Restricted cash included in other long-term assets	21,594		22,127
Total cash, cash equivalents and restricted cash	$	64,833	$	40,701