Investments (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Investments with maturity greater than one year	$ 0	$ 0
Short-term Debt
Debt Securities, Available-for-sale [Line Items]
Cost	43,787,000	43,815,000
Unrealized Gross Gains	12,000	32,000
Unrealized Gross Losses	(3,000)	(3,000)
Fair Value	43,796,000	43,844,000
Commercial paper \| Short-term Debt
Debt Securities, Available-for-sale [Line Items]
Cost	13,286,000	13,275,000
Unrealized Gross Gains	0	0
Unrealized Gross Losses	0	0
Fair Value	13,286,000	13,275,000
Corporate bonds \| Short-term Debt
Debt Securities, Available-for-sale [Line Items]
Cost	6,509,000	6,543,000
Unrealized Gross Gains	0	0
Unrealized Gross Losses	(3,000)	(3,000)
Fair Value	6,506,000	6,540,000
U.S. government securities \| Short-term Debt
Debt Securities, Available-for-sale [Line Items]
Cost	23,992,000	23,997,000
Unrealized Gross Gains	12,000	32,000
Unrealized Gross Losses	0	0
Fair Value	$ 24,004,000	$ 24,029,000

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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