FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Summary of Assets and Liabilities Measured at Fair Value (Details) - Recurring Fair Value Measurements $ in Thousands	Dec. 31, 2020 USD ($)
Assets:
Short-term investments	$ 149,822
Cash and cash equivalents	373,980
Investments	12,049
Other current assets	45,688
Other assets	2,985
Total assets measured at fair value	584,524
Liabilities:
Contingent earnout liability	8,973
Certificates of deposit
Assets:
Short-term investments	12
Corporate and municipal debt securities
Assets:
Short-term investments	144,780
U.S. government and federal agency securities
Assets:
Short-term investments	5,030
Level 1
Assets:
Short-term investments	5,030
Cash and cash equivalents	373,980
Investments	10,206
Other current assets	45,688
Other assets	2,985
Total assets measured at fair value	437,889
Liabilities:
Contingent earnout liability	0
Level 1 | Certificates of deposit
Assets:
Short-term investments	0
Level 1 | Corporate and municipal debt securities
Assets:
Short-term investments	0
Level 1 | U.S. government and federal agency securities
Assets:
Short-term investments	5,030
Level 2
Assets:
Short-term investments	144,792
Cash and cash equivalents	0
Investments	343
Other current assets	0
Other assets	0
Total assets measured at fair value	145,135
Liabilities:
Contingent earnout liability	0
Level 2 | Certificates of deposit
Assets:
Short-term investments	12
Level 2 | Corporate and municipal debt securities
Assets:
Short-term investments	144,780
Level 2 | U.S. government and federal agency securities
Assets:
Short-term investments	0
Level 3
Assets:
Short-term investments	0
Cash and cash equivalents	0
Investments	1,500
Other current assets	0
Other assets	0
Total assets measured at fair value	1,500
Liabilities:
Contingent earnout liability	8,973
Level 3 | Certificates of deposit
Assets:
Short-term investments	0
Level 3 | Corporate and municipal debt securities
Assets:
Short-term investments	0
Level 3 | U.S. government and federal agency securities
Assets:
Short-term investments	$ 0