Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

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The Company and Summary of Significant Accounting Policies - Impairment of Investments (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Impairment charge		$ 0	$ 0	$ 0
Investments, equity method		$ 6,376,000	5,961,000
Germanium materials
Schedule of Equity Method Investments [Line Items]
Impairment charge	$ 1,100,000		1,100,000
Xilingol Tongli Germanium Co. Ltd Investment \| Xilingol Tongli Germanium Co. Ltd Investment
Schedule of Equity Method Investments [Line Items]
Ownership (as a percent)		25.00%
Investments, equity method		$ 0	$ 0