FAIR VALUE MEASUREMENT - Additional information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 33,464,000	$ 38,837,000	$ 57,349,000
Change in fair value of contingent consideration	5,327,000	28,402,000	10,788,000
Additions	0	0	19,700,000
Payments	(30,542,000)	(33,775,000)	(49,000,000)
Ending balance	8,249,000	$ 33,464,000	$ 38,837,000
Minimum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration on acquisition date	0
Maximum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contingent consideration on acquisition date	$ 23,400,000