Supplemental Financial Information - Other Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Other current liabilities:
Current portion of operating lease obligations	$ 2,382		$ 0
Accrued interest	213		407
Income and other taxes payable	678		479
Other current liabilities	1,038		1,252
Total other current liabilities	4,311		2,138
Other long-term liabilities:
Operating lease obligations, long-term	2,810		0
Mine reclamation liability	2,721		624
Other	229		316
Total other long-term liabilities	$ 5,760	$ 4,811	$ 940