Investments (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Marketable Securities [Line Items]
Amortized Cost	$ 63,996,000		$ 63,996,000		$ 66,272,000
Gains	0		0		20,000
Losses	(23,000)		(23,000)		0
Credit Losses	0		0		(6,000)
Estimated Fair Value	63,973,000		$ 63,973,000		$ 66,286,000
Remaining contractual maturity period			3 years		3 years
Impairments of assets	0	$ 0	$ 0	$ 0
Short-term investments
Marketable Securities [Line Items]
Estimated Fair Value	43,738,000		43,738,000		$ 42,187,000
Long-term investments
Marketable Securities [Line Items]
Estimated Fair Value	20,235,000		20,235,000		24,099,000
Commercial paper
Marketable Securities [Line Items]
Amortized Cost	13,243,000		13,243,000		8,993,000
Gains	0		0		1,000
Losses	(1,000)		(1,000)		0
Credit Losses	0		0		0
Estimated Fair Value	13,242,000		13,242,000		8,994,000
Corporate notes
Marketable Securities [Line Items]
Amortized Cost	48,178,000		48,178,000		35,917,000
Gains	0		0		0
Losses	(22,000)		(22,000)		0
Credit Losses	0		0		(6,000)
Estimated Fair Value	48,156,000		48,156,000		35,911,000
U.S. government securities
Marketable Securities [Line Items]
Amortized Cost	1,500,000		1,500,000		12,828,000
Gains	0		0		14,000
Losses	0		0		0
Credit Losses	0		0		0
Estimated Fair Value	1,500,000		1,500,000		12,842,000
U.S. government agency bonds
Marketable Securities [Line Items]
Amortized Cost	1,075,000		1,075,000		5,000,000
Gains	0		0		1,000
Losses	0		0		0
Credit Losses	0		0		0
Estimated Fair Value	$ 1,075,000		$ 1,075,000		5,001,000
U.S. asset-backed securities
Marketable Securities [Line Items]
Amortized Cost					3,534,000
Gains					4,000
Losses					0
Credit Losses					0
Estimated Fair Value					$ 3,538,000