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Asset Retirement Obligation | 12 Months Ended
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Dec. 31, 2017
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligation | 12. Asset Retirement Obligation The Company had recorded a post-closure reclamation and site restoration obligation of $8,982 at December 31, 2017. The following is a reconciliation of the total reclamation liability for asset retirement obligations.
Balance at December 31, 2015 |  | $ | 1,180 |
Additions and revisions of prior estimates |  |  | 399 |
Reductions to liabilities due to revision of estimates |  |  | (211 | )
Accretion expenses |  |  | 16 |
Balance at December 31, 2016 |  | $ | 1,384 |
Additions and revisions of prior estimates |  |  | 7,084 |
Accretion expenses |  |  | 514 |
Balance at December 31, 2017 |  | $ | 8,982 |
During the fourth quarter of 2017, the Company reduced the expected mining period for a certain phase of its operations. This change in estimate resulted in an approximate $4,511 increase to the liability.

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- Definition The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -URI http://asc.fasb.org/subtopic&trid=2175671 + Details
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