INCOME TAXES (Deferred Income Taxes) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred Tax Assets, Gross [Abstract]
Property and equipment	$ 8,164	$ 5,329
Intangible assets	827	574
Accrued expenses	50,639	41,457
Net operating loss carryforward	6,089	5,168
Deferred revenue	9,796	3,510
Stock-based compensation	30,112	29,596
Operating lease liabilities	51,519	7,438
Foreign tax credit	2,168	3,491
Foreign currency exchange	4,890	2,499
Other assets	1,252	1,533
Deferred tax assets	165,456	100,595
Less: valuation allowance	(5,485)	(3,877)
Total deferred tax assets	159,971	96,718
Deferred Tax Liabilities, Gross [Abstract]
Property and equipment	3,818	4,981
Intangible assets	12,018	11,364
Operating lease right-of-use assets	50,149	6,900
Accrued revenue and expenses	991	2,176
U.S. taxation of foreign subsidiaries	1,608	0
Foreign currency exchange	1,153	375
Other liabilities	1,095	437
Total deferred tax liabilities	70,832	26,233
Net deferred tax assets	89,139	70,485
Other noncurrent liabilities
Deferred Tax Liabilities, Gross [Abstract]
Deferred Income Tax Liabilities, Net	3,300	4,500
Business acquisitions
Deferred Tax Assets, Gross [Abstract]
Stock-based compensation	$ 6,100	$ 6,800
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