SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, STOCK BASED COMPENSATION EXPENSE (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense	$ 9,527	$ 13,816	$ 24,707	$ 25,845
Ten-X [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense			700
Cost of Revenues [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense	2,530	2,560	5,002	4,618
Selling and Marketing (excluding customer base amortization) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense	1,770	1,765	3,794	3,404
Software Development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense	2,287	2,339	4,815	4,395
General and Administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Compensation expense	$ 2,940	$ 7,152	$ 11,096	$ 13,428