Description of Business and Summary of Significant Accounting Policies - Cash and cash equivalents (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Description of Business and Summary of Significant Accounting Policies
Restricted cash equivalents	$ 300
Cash and cash equivalents	410,217	$ 196,046
Restricted cash - current	4,614	11,407
Restricted Cash, Noncurrent	1,000
Cash, cash equivalents and restricted cash	$ 415,831	$ 207,453	$ 8,137	$ 7,179