INCOME TAXES (Deferred Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Deferred Tax Assets, Gross [Abstract]
Property and equipment	$ 4,531	$ 170
Intangible assets	1,262	1,456
Accrued expenses	32,067	4,392
Net operating loss carryforward	4,983	5,069
Deferred revenue	5,802	1,280
Stock-based compensation	27,558	16,197
Foreign currency exchange	5,772	0
Other assets	782	1,415
Deferred tax assets	82,757	29,979
Less: valuation allowance	(3,189)	(924)
Total deferred tax assets	79,568	29,055
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	1,480	1,868
Intangible assets	5,582	3,077
Accrued revenue and expenses	1,540	1,352
U.S. taxation of foreign subsidiaries	3,000	0
Subsidiary withholding tax liability	0	4,850
Stock-based compensation	0	1,498
Other liabilities	933	239
Total deferred tax liabilities	12,535	12,884
Net deferred tax assets	67,033	16,171
Other Noncurrent Liabilities
Deferred Tax Liabilities, Classification [Abstract]
Deferred tax liabilities, noncurrent	2,950	8,803
Business acquisitions
Deferred Tax Assets, Gross [Abstract]
Stock-based compensation	$ 7,561	$ 8,512
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