Fair Value Measurements - Fair Value Hierarchy (Details) - Fair Value, Measurements, Recurring - USD ($)	Sep. 30, 2022	Dec. 31, 2021
Assets
Total assets	$ 311,421,000	$ 324,967,000
Liabilities
Total liabilities	7,444,000	7,302,000
Fair Value, Inputs, Level 1
Assets
Total assets	46,243,000	4,212,000
Fair Value, Inputs, Level 2
Assets
Total assets	265,178,000	320,755,000
Liabilities
Total liabilities	7,444,000	7,302,000
Fair Value, Inputs, Level 3
Assets
Total assets	0	0
Liabilities
Total liabilities	0	0
Money market funds
Assets
Total assets	46,243,000	4,212,000
Money market funds | Fair Value, Inputs, Level 1
Assets
Total assets	46,243,000	4,212,000
U.S. Government agency bonds
Assets
Total assets	85,703,000	123,271,000
U.S. Government agency bonds | Fair Value, Inputs, Level 2
Assets
Total assets	85,703,000	123,271,000
U.S. Government bonds
Assets
Total assets	75,825,000	76,525,000
U.S. Government bonds | Fair Value, Inputs, Level 2
Assets
Total assets	75,825,000	76,525,000
Bank certificates of deposit
Assets
Total assets	5,478,000	12,492,000
Bank certificates of deposit | Fair Value, Inputs, Level 2
Assets
Total assets	5,478,000	12,492,000
Commercial paper.
Assets
Total assets		2,997,000
Commercial paper. | Fair Value, Inputs, Level 2
Assets
Total assets		2,997,000
Corporate notes
Assets
Total assets	47,110,000	55,032,000
Corporate notes | Fair Value, Inputs, Level 2
Assets
Total assets	47,110,000	55,032,000
Asset-backed securities
Assets
Total assets	25,575,000	23,774,000
Asset-backed securities | Fair Value, Inputs, Level 2
Assets
Total assets	25,575,000	23,774,000
Municipal bonds
Assets
Total assets	17,909,000	19,252,000
Municipal bonds | Fair Value, Inputs, Level 2
Assets
Total assets	17,909,000	19,252,000
Investments held for deferred compensation plans
Assets
Total assets	7,578,000	7,412,000
Liabilities
Total liabilities	7,444,000	7,302,000
Investments held for deferred compensation plans | Fair Value, Inputs, Level 2
Assets
Total assets	7,578,000	7,412,000
Liabilities
Total liabilities	$ 7,444,000	$ 7,302,000