INCOME TAXES (Deferred Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Gross [Abstract]
Property and equipment	$ 170	$ 203
Intangible assets	1,456	1,525
Accrued expenses	4,392	9,172
Net operating loss carryforward	5,069	5,368
Deferred revenue	1,280	1,165
Stock-based compensation	16,197	19,701
Other assets	1,415	17
Deferred tax assets	29,979	37,151
Less: valuation allowance	(924)	0
Total deferred tax assets	29,055	37,151
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	1,868	1,735
Intangible assets	3,077	4,969
Accrued revenue and expenses	1,352	500
Subsidiary withholding tax liability	4,850	0
Stock-based compensation	1,498	1,606
Other liabilities	239	314
Total deferred tax liabilities	12,884	9,124
Net deferred tax assets	16,171	28,027
Other noncurrent liabilities
Deferred Tax Liabilities, Classification [Abstract]
Deferred tax liabilities, noncurrent	8,803	2,979
Business acquisitions
Deferred Tax Assets, Gross [Abstract]
Stock-based compensation	$ 8,512	$ 11,471
Business acquisitions | Minimum
Deferred Tax Assets, Gross [Abstract]
Amortization period of stock-based compensation for tax	10 years
Business acquisitions | Maximum
Deferred Tax Assets, Gross [Abstract]
Amortization period of stock-based compensation for tax	15 years