Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
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	105,960,516	105,448,921
Common Stock, Shares Outstanding	105,960,516	105,448,921
Marketable securities, Amortized Cost	$ 494,000	$ 811,277
Marketable Securities, Allowance for Credit Loss	124	0
Restricted Debt Securities [Member]
Marketable securities, Amortized Cost	243,367	229,199
Marketable Securities, Allowance for Credit Loss	$ 0	$ 0