Financial Instruments - Summary of Marketable Securities (Details) - USD ($)	Mar. 31, 2020	Dec. 31, 2019
Marketable Securities [Line Items]
Debt securities, Cost	$ 33,932,000	$ 45,782,000
Debt securities, Gross Unrealized Gains	17,000	33,000
Debt securities, Gross Unrealized Losses	(272,000)	(13,000)
Debt securities, Allowance for Credit Losses	0
Debt securities, Estimated Fair Values	33,677,000	45,802,000
Equity securities, Cost	38,196,000	6,006,000
Equity securities, Gross Unrealized Gains	0	0
Equity securities, Gross Unrealized Losses	(3,015,000)	(2,281,000)
Equity securities, Allowance for Credit Losses	0
Equity securities, Estimated Fair Values	35,181,000	3,725,000
Marketable securities, Cost	72,128,000	51,788,000
Marketable securities, Gross Unrealized Gains	17,000	33,000
Marketable securities, Gross Unrealized Losses	(3,287,000)	(2,294,000)
Marketable securities, Allowance for Credit Losses	0
Marketable securities, Estimated Fair Values	68,858,000	49,527,000
Corporate bonds and notes
Marketable Securities [Line Items]
Debt securities, Cost	32,608,000	41,730,000
Debt securities, Gross Unrealized Gains	16,000	29,000
Debt securities, Gross Unrealized Losses	(272,000)	(13,000)
Debt securities, Allowance for Credit Losses	0
Debt securities, Estimated Fair Values	32,352,000	41,746,000
Commercial paper
Marketable Securities [Line Items]
Debt securities, Cost	1,324,000	4,052,000
Debt securities, Gross Unrealized Gains	1,000	4,000
Debt securities, Gross Unrealized Losses	0	0
Debt securities, Allowance for Credit Losses	0
Debt securities, Estimated Fair Values	1,325,000	4,056,000
Marketable equity securities
Marketable Securities [Line Items]
Equity securities, Cost	3,405,000	3,405,000
Equity securities, Gross Unrealized Gains	0	0
Equity securities, Gross Unrealized Losses	(3,015,000)	(2,281,000)
Equity securities, Allowance for Credit Losses	0
Equity securities, Estimated Fair Values	390,000	1,124,000
Money market funds
Marketable Securities [Line Items]
Equity securities, Cost	34,791,000	2,601,000
Equity securities, Gross Unrealized Gains	0	0
Equity securities, Gross Unrealized Losses	0	0
Equity securities, Allowance for Credit Losses	0
Equity securities, Estimated Fair Values	34,791,000	2,601,000
Cash and cash equivalents
Marketable Securities [Line Items]
Marketable securities, Estimated Fair Values	34,791,000	2,601,000
Available-for-sale debt securities
Marketable Securities [Line Items]
Marketable securities, Estimated Fair Values	33,677,000	45,802,000
Equity securities
Marketable Securities [Line Items]
Marketable securities, Estimated Fair Values	$ 390,000	$ 1,124,000