FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Summary of Assets and Liabilities Measured at Fair Value (Details) - Recurring Fair Value Measurements $ in Thousands	Jun. 30, 2020 USD ($)
Assets:
Short-term investments	$ 65,787
Cash and cash equivalents	426,245
Investments	8,940
Other current assets	46,643
Other assets	3,336
Total assets measured at fair value	550,951
Liabilities:
Contingent earnout liability	12,723
Level 1
Assets:
Short-term investments	18,859
Cash and cash equivalents	426,245
Investments	8,597
Other current assets	46,643
Other assets	3,336
Total assets measured at fair value	503,680
Liabilities:
Contingent earnout liability	0
Level 2
Assets:
Short-term investments	46,928
Cash and cash equivalents	0
Investments	343
Other current assets	0
Other assets	0
Total assets measured at fair value	47,271
Liabilities:
Contingent earnout liability	0
Level 3
Assets:
Short-term investments	0
Cash and cash equivalents	0
Investments	0
Other current assets	0
Other assets	0
Total assets measured at fair value	0
Liabilities:
Contingent earnout liability	12,723
Certificates of deposit
Assets:
Short-term investments	1,743
Certificates of deposit | Level 1
Assets:
Short-term investments	0
Certificates of deposit | Level 2
Assets:
Short-term investments	1,743
Certificates of deposit | Level 3
Assets:
Short-term investments	0
Corporate and municipal debt securities
Assets:
Short-term investments	45,185
Corporate and municipal debt securities | Level 1
Assets:
Short-term investments	0
Corporate and municipal debt securities | Level 2
Assets:
Short-term investments	45,185
Corporate and municipal debt securities | Level 3
Assets:
Short-term investments	0
U.S. government and federal agency securities
Assets:
Short-term investments	18,859
U.S. government and federal agency securities | Level 1
Assets:
Short-term investments	18,859
U.S. government and federal agency securities | Level 2
Assets:
Short-term investments	0
U.S. government and federal agency securities | Level 3
Assets:
Short-term investments	$ 0