Cash, Cash Equivalents and Investments - Investment Category and Length (Details)	12 Months Ended
	Dec. 31, 2020 USD ($) company	Dec. 31, 2019 USD ($) subsidiary company	Dec. 31, 2018 USD ($)
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	$ 2,048,000	$ 4,515,000
Gross unrealized loss, in loss position less than twelve months	(2,000)	(9,000)
Fair value, total in loss position	2,048,000	4,515,000
Gross unrealized loss, total in loss position	(2,000)	(9,000)
Minority Investments
Investments, equity method	$ 6,376,000	$ 5,961,000
Number of consolidated subsidiaries | subsidiary		1
Number of equity method investments | company	5	5
Impairment charge	$ 0	$ 0	$ 0
Xilingol Tongli Germanium Co. Ltd Investment | Xilingol Tongli Germanium Co. Ltd Investment
Minority Investments
Investments, equity method	$ 0	0
Ownership (as a percent)	25.00%
Corporate Bonds [Member]
Summary of fair value and gross unrealized losses related to available-for-sale securities [Abstract]
Fair value, in loss position less than twelve months	$ 2,048,000	4,515,000
Gross unrealized loss, in loss position less than twelve months	(2,000)	(9,000)
Fair value, total in loss position	2,048,000	4,515,000
Gross unrealized loss, total in loss position	(2,000)	(9,000)
Other assets
Minority Investments
Investments, equity method	$ 6,400,000	$ 6,000,000.0