Supplemental Financial Information

Supplemental Balance Sheet Information

The following table summarizes the components of Prepaid expenses and other assets and Other long-term assets, net as presented in the Condensed Consolidated Balance Sheets:



	As of
(in thousands)	June 30, 2019		December 31, 2018
Prepaid expenses and other assets:
Prepaid expenses	$	1,904	$	1,233
Prepaid income taxes	1,970		2,940
Other	1,724		1,397
	$	5,598	$	5,570
Other long-term assets:
Highview Investment	$	552	$	552
Spare parts	3,222		3,278
Mine development costs, net	3,167		2,531
Mine reclamation asset, net	2,390		—
Prepaid royalty expense, long-term	955		955
Right of use assets, operating leases, net	5,488		—
Other long-term assets	779		677
	$	16,553	$	7,993

Spare parts include critical spares required to support plant operations. Parts and supply costs are determined using the lower of cost or estimated replacement cost. Parts are recorded as maintenance expenses in the period in which they are consumed.

Mine development costs include acquisition costs, the cost of other development work and mitigation costs related to the Company's mining operations which are depleted over the estimated life of the related mine reserves, which is 18 years. The Company performs an evaluation of the recoverability of the carrying value of mine development costs to determine if facts and circumstances indicate that their carrying value may be impaired and if any adjustment is warranted. There were no indicators of impairment as of June 30, 2019. Mine reclamation asset represents an asset retirement obligation asset and is depreciated over the estimated life of the mine, which is 18 years.

The Company holds a long-term investment (the "Highview Investment") in Highview Enterprises Limited ("Highview"), a London, England based developmental stage company specializing in power storage. In November 2014, the Company acquired an 8% ownership interest in the common stock of Highview for $2.8 million in cash. The Company accounts for the Highview Investment as an investment recorded at cost, less impairment, plus or minus observable changes in price for identical or similar investments of the same issuer.

The Highview Investment is evaluated for indicators of impairment such as an event or change in circumstances that may have a significant adverse effect on the fair value of the investment. There were no changes to the carrying value of the Highview Investment for the three and six months ended June 30, 2019 as there were no indicators of impairment or observable price changes for equity issued by Highview.

The following table details the components of Other current liabilities and Other long-term liabilities as presented in the Condensed Consolidated Balance Sheets:



	As of
(in thousands)	June 30, 2019		December 31, 2018
Other current liabilities:
Current portion of operating lease obligations	$	2,725	$	—
Accrued interest	996		407
Income and other taxes payable	909		479
Other	922		1,252
	$	5,552	$	2,138
Other long-term liabilities:
Operating lease obligations, long-term	$	2,824	$	—
Mine reclamation liability	2,490		624
Other long-term liabilities	135		316
	$	5,449	$	940

Supplemental Condensed Consolidated Statements of Operations Information

The following table details the components of Interest expense in the Condensed Consolidated Statements of Operations:



	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2019		2018		2019		2018
Interest on Senior Term Loan	$	1,134	$	—	$	2,404	$	—
Debt discount and debt issuance costs	470		—		851		—
453A interest	326		404		648		740
Other	57		8		188		8
	$	1,987	$	412	$	4,091	$	748