Fair Value Measurements (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	$ 0		$ 0
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	0		$ 0
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	122,756,000	$ 146,311,000
Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	105,629,000	60,295,000
Recurring [Member] | Commercial Papers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	2,000,000	39,577,000
Recurring [Member] | Corporate Bonds/Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		7,969,000
Recurring [Member] | U.S. Government Securitie [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	15,127,000	38,470,000
Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	105,629,000	60,295,000
Recurring [Member] | Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	105,629,000	60,295,000
Recurring [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	17,127,000	86,016,000
Recurring [Member] | Level 2 [Member] | Commercial Papers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	2,000,000	39,577,000
Recurring [Member] | Level 2 [Member] | Corporate Bonds/Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets		7,969,000
Recurring [Member] | Level 2 [Member] | U.S. Government Securitie [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 15,127,000	$ 38,470,000