SIGNIFICANT ACCOUNTING POLICIES - Marketable Securities (Details) - USD ($) $ in Thousands |
Sep. 30, 2021 |
Dec. 31, 2020 |
---|---|---|
Marketable Securities [Line Items] | ||
Marketable securities | $ 144,932 | $ 25,736 |
U.S. Treasury securities | ||
Marketable Securities [Line Items] | ||
Marketable securities | 76,591 | 25,736 |
Commercial paper (A-1 or P-1 rated) | ||
Marketable Securities [Line Items] | ||
Marketable securities | $ 68,341 | $ 0 |