Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Common Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Common Stock, Shares Authorized	500,000,000	500,000,000
Common Stock, Shares Issued	106,318,905	105,980,466
Common Stock, Shares Outstanding	106,318,905	105,980,466
Marketable securities, Amortized Cost	$ 418,450	$ 519,844
Marketable Securities, Allowance for Credit Loss	87	121
Restricted Debt Securities [Member]
Marketable securities, Amortized Cost	0	247,628
Marketable Securities, Allowance for Credit Loss	$ 0	$ 13