FAIR VALUE MEASUREMENTS (Reconciliation of Acquisition-Related Contractual Contingent Liabilities Using Significant Unobservable Inputs) (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Jun. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Continuum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value of contingent consideration	$ (396)	$ (900)
Think
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value of contingent consideration			$ 2,172
Level 3
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Contractual contingent liabilities, beginning of period			7,468	$ 0	$ 0
Settlements of contractual contingent liabilities			1,104
Other activity related to contractual contingent liabilities				0	0
Effect of net foreign currency exchange rate changes			255	(22)
Contractual contingent liabilities, end of period			10,495	7,468	$ 0
Level 3 | Interest and Other Income, net
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value of contingent consideration			1,776	(900)
Level 3 | Continuum
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition date fair value				2,400
Level 3 | Think
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition date fair value				$ 5,990
Level 3 | Other 2019 Acquisitions
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Acquisition date fair value			$ 2,100