Fair Value Measurements (Fair Value Hierarchy for Assets and Liabilities Measured at Fair Value on Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 33,904	$ 26,901
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	33,904	26,901
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Cash equivalents (money market funds)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	33,904	26,901
Cash equivalents (money market funds) | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	33,904	26,901
Cash equivalents (money market funds) | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	0	0
Cash equivalents (money market funds) | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Assets measured at fair value on a recurring basis	$ 0	$ 0