FAIR VALUE MEASUREMENT (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 31, 2018	Jun. 11, 2018	Sep. 19, 2017	Jun. 14, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ 57,349,000	$ 23,100,000	$ 0
Change in fair value of contingent consideration	$ 6,800,000	10,788,000	23,931,000	0
Contingent consideration additions		19,700,000	11,318,000	23,100,000
Contingent consideration payments		(49,000,000)	(1,000,000)	0
Ending balance	$ 38,837,000	$ 38,837,000	$ 57,349,000	$ 23,100,000
Minimum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent consideration on acquisition date					$ 0	$ 0	$ 3,000,000.0	$ 3,000,000.0
Maximum [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent consideration on acquisition date					$ 70,200,000	$ 8,750,000	$ 9,000,000	$ 4,000,000