Statements of Cash Flows (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract]
Cash and cash equivalents	$ 304,962	$ 166,130
Restricted cash	0	928
Total cash, cash equivalents and restricted cash shown on the statements of cash flows	$ 304,962	$ 167,058	$ 36,973	$ 34,468