FAIR VALUE MEASUREMENTS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Oct. 31, 2018	Jun. 11, 2018	Sep. 19, 2017	Jun. 14, 2017	May 31, 2017
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Annual interest rate on convertible senior notes							0.625%
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 38,837,000	$ 57,349,000
Change in fair value of contingent consideration	14,592,000	(741,000)
Contingent consideration additions	0	0
Contingent consideration payments	(4,000,000)	(23,500,000)
Ending balance	$ 49,429,000	$ 33,108,000
Minimum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent consideration			$ 0	$ 0	$ 0	$ 2,000,000.0
Maximum
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Contingent consideration			$ 70,200,000	$ 8,750,000	$ 6,000,000	$ 3,000,000