PROPERTY AND EQUIPMENT, NET (Property and Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 181,005	$ 148,125
Less accumulated depreciation and amortization	(78,359)	(61,706)
Total	102,646	86,419	$ 73,616
Depreciation and amortization expenses	$ 28,539	21,000	$ 15,217
Computer hardware
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	3 years
Property and equipment, gross	$ 74,884	62,132
Building
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	49 years
Property and equipment, gross	$ 34,458	34,058
Leasehold improvements
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	9 years
Property and equipment, gross	$ 25,036	13,186
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	7 years
Property and equipment, gross	$ 21,544	18,071
Office equipment
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	7 years
Property and equipment, gross	$ 13,203	10,825
Purchased computer software
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	4 years
Property and equipment, gross	$ 10,406	8,379
Land improvements
Property, Plant and Equipment [Line Items]
Weighted average useful life (in years)	20 years
Property and equipment, gross	$ 1,474	$ 1,474