INCOME TAXES (Deferred Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets, Gross [Abstract]
Property and equipment	$ 5,329	$ 4,531
Intangible assets	574	1,262
Accrued expenses	41,457	32,067
Net operating loss carryforward	5,168	4,983
Deferred revenue	3,510	5,802
Stock-based compensation	29,596	27,558
Operating lease liabilities	7,438	0
Foreign tax credit	3,491	0
Foreign currency exchange	2,499	5,772
Other assets	1,533	782
Deferred tax assets	100,595	82,757
Less: valuation allowance	(3,877)	(3,189)
Total deferred tax assets	96,718	79,568
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	4,981	1,480
Intangible assets	11,364	5,582
Operating lease right-of-use assets	6,900	0
Accrued revenue and expenses	2,176	1,540
U.S. taxation of foreign subsidiaries	0	3,000
Other liabilities	812	933
Total deferred tax liabilities	26,233	12,535
Net deferred tax assets	70,485	67,033
Other Noncurrent Liabilities
Deferred Tax Liabilities, Classification [Abstract]
Deferred tax liabilities, noncurrent	4,530	2,950
Business acquisitions
Deferred Tax Assets, Gross [Abstract]
Stock-based compensation	$ 6,788	$ 7,561
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