FAIR VALUE MEASUREMENTS - Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Assets:
Total	$ 328,893	$ 24,157
Liabilities:
Derivative liabilities		16
Total		16
Money market funds
Assets:
Cash equivalents:	52,018	24,157
Commercial paper
Assets:
Investments:	69,968
Corporate bonds
Assets:
Investments:	186,863
U.S. Government agencies
Assets:
Investments:	20,044
Level 1
Assets:
Total	52,018	24,157
Liabilities:
Derivative liabilities		0
Total		0
Level 1 | Money market funds
Assets:
Cash equivalents:	52,018	24,157
Level 1 | Commercial paper
Assets:
Investments:	0
Level 1 | Corporate bonds
Assets:
Investments:	0
Level 1 | U.S. Government agencies
Assets:
Investments:	0
Level 2
Assets:
Total	276,875	0
Liabilities:
Derivative liabilities		0
Total		0
Level 2 | Money market funds
Assets:
Cash equivalents:	0	0
Level 2 | Commercial paper
Assets:
Investments:	69,968
Level 2 | Corporate bonds
Assets:
Investments:	186,863
Level 2 | U.S. Government agencies
Assets:
Investments:	20,044
Level 3
Assets:
Total	0	0
Liabilities:
Derivative liabilities		16
Total		16
Level 3 | Money market funds
Assets:
Cash equivalents:	0	$ 0
Level 3 | Commercial paper
Assets:
Investments:	0
Level 3 | Corporate bonds
Assets:
Investments:	0
Level 3 | U.S. Government agencies
Assets:
Investments:	$ 0