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Significant Accounting Policies - Concentrations (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Concentration risk
Cash and cash equivalents	$ 37,747	$ 70,162	$ 106,794
Investments - debt securities	40,576	$ 88,956
Credit concentration risk \| Assets
Concentration risk
Cash amount not insured by FDIC	15,200
Credit concentration risk \| Assets \| Money market fund
Concentration risk
Cash and cash equivalents	19,200
Credit concentration risk \| Assets \| U.S. Treasury Bills
Concentration risk
Investments - debt securities	$ 40,600