SEGMENT REPORTING, ASSETS AND LIABILITIES (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property and equipment, net	$ 85,978	$ 83,303
Goodwill	1,612,065	1,611,535	$ 1,283,457
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	3,548,284	3,312,957
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	419,670	291,015
North America [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	81,867	79,493
Goodwill	1,573,088	1,573,088	1,253,494
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	3,475,272	3,253,035
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	386,122	272,776
International [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	4,111	3,810
Goodwill	38,977	38,447	$ 29,963
Reconciliation of operating segment assets to total assets [Abstract]
Total assets	73,012	59,922
Reconciliation of operating segment liabilities to total liabilities [Abstract]
Total liabilities	$ 33,548	$ 18,239