Fair Value of Financial Instruments (Details) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	$ 398,119,000	$ 441,186,000
Equity method investment, ownership percentage	25.00%	25.00%
Equity method investment	$ 1,800,000	$ 2,800,000
Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	7,402,000	18,162,000
U.S. Government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	102,812,000	169,633,000
Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	287,905,000	253,391,000
Recurring basis
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	398,119,000	441,186,000
Recurring basis | Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	7,402,000	18,162,000
Recurring basis | U.S. Government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	102,812,000	169,633,000
Recurring basis | Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	287,905,000	253,391,000
Recurring basis | Quoted market prices in active markets (Level 1)
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	7,402,000	18,162,000
Recurring basis | Quoted market prices in active markets (Level 1) | Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	7,402,000	18,162,000
Recurring basis | Quoted market prices in active markets (Level 1) | U.S. Government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Quoted market prices in active markets (Level 1) | Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Significant other observable inputs (Level 2)
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	390,717,000	423,024,000
Recurring basis | Significant other observable inputs (Level 2) | Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Significant other observable inputs (Level 2) | U.S. Government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	102,812,000	169,633,000
Recurring basis | Significant other observable inputs (Level 2) | Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	287,905,000	253,391,000
Recurring basis | Significant unobservable inputs (Level 3)
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Significant unobservable inputs (Level 3) | Money market funds
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Significant unobservable inputs (Level 3) | U.S. Government bonds and notes
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	0	0
Recurring basis | Significant unobservable inputs (Level 3) | Corporate notes, bonds and commercial paper
Financial assets subject to fair value measurements and the necessary disclosures
Fair value	$ 0	$ 0