FAIR VALUE MEASUREMENTS - Financial Assets And Liabilities Measured At Fair Value On Recurring Basis (Details) - Fair value, measurements, recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	$ 5,605	$ 8,566
Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	17,607	27,683
Money market funds
Assets:
Fair value of financial assets measured on recurring basis	181,443	214,120
Level 1 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 1 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 1 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	181,443	214,120
Level 2 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 2 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	0	0
Level 2 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	0	0
Level 3 Inputs | Acquisition-related contingent consideration—current
Liabilities:
Fair value of financial liabilities measured on recurring basis	5,605	8,566
Level 3 Inputs | Acquisition-related contingent consideration—noncurrent
Liabilities:
Fair value of financial liabilities measured on recurring basis	17,607	27,683
Level 3 Inputs | Money market funds
Assets:
Fair value of financial assets measured on recurring basis	$ 0	$ 0