Fair Value Measurements - Fair Value by Contractual Maturity (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
One Year or Less	$ 19,424,000
Over One Year Through Five Years	30,951,000
Over Five Years	0
Total	50,375,000	$ 0
U.S. Treasury securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
One Year or Less	3,033,000
Over One Year Through Five Years	15,373,000
Over Five Years	0
Total	18,406,000
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
One Year or Less	13,734,000
Over One Year Through Five Years	0
Over Five Years	0
Total	13,734,000
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
One Year or Less	0
Over One Year Through Five Years	9,921,000
Over Five Years	0
Total	9,921,000
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
One Year or Less	2,657,000
Over One Year Through Five Years	5,657,000
Over Five Years	0
Total	$ 8,314,000