ASSET RETIREMENT OBLIGATIONS AND RESTRICTED CASH

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



	March 31, 2017			December 31, 2016
Asset retirement obligation, beginning of period	$	17,033		$	8,573
Revision of estimate	—			4,186
Acquired in asset acquisitions or business combinations	—			5,454
Accretion of liabilities	345			906
Settlements	(97		)	(2,086		)
Asset retirement obligation, end of period	$	17,281		$	17,033
Asset retirement obligation:
Current	$	32		$	32
Non-current	17,249			17,001
Asset retirement obligation, end of period	$	17,281		$	17,033

Revision of estimates is as a result of a change in estimates of the amount or timing of cash flows to settle asset retirement obligations. Changes to the asset retirement obligations are recorded in profit and loss.

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% (December 31, 2016 – 2.0%). The total undiscounted decommissioning liability at March 31, 2017 is $43.00 million (December 31, 2016 - $43.00 million). Reclamation costs are expected to be incurred between 2017 and 2039 in the following manner: 2017 – 2021 - $8.21 million, 2022 – 2026 - $11.22 million, 2027 – 2031 - $3.65 million, 2032 – 2036 - $11.95 million, 2037 – 2039 - $7.97 million.

The following table summarizes the Company’s restricted cash:



	March 31, 2017			December 31, 2016
Restricted cash, beginning of period	$	23,175		$	12,980
Restricted cash from acquisitions	—			4,532
Additional collateral posted	—			5,663
Release of collateral related to change in surety agents	(10,811		)	—
Posting of collateral with new surety agents	12,725			—
Restricted cash, end of period	$	25,089		$	23,175

The Company has cash, cash equivalents and fixed income securities as collateral for various bonds posted in favor of the State of Utah, the State of Wyoming, the applicable state regulatory agencies in Colorado and Arizona and the U.S. Bureau of Land Management for estimated reclamation costs associated with the White Mesa Mill, Nichols Ranch, Alta Mesa and 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.