SEGMENT AND GEOGRAPHIC DISCLOSURES - Geographic Breakdown of Revenues (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenues from External Customers [Line Items]
Total revenues	$ 302,385	$ 286,554
United States
Revenues from External Customers [Line Items]
Total revenues	233,376	215,212
Canada
Revenues from External Customers [Line Items]
Total revenues	27,368	27,248
Europe
Revenues from External Customers [Line Items]
Total revenues	28,225	25,999
Other foreign countries
Revenues from External Customers [Line Items]
Total revenues	$ 13,416	$ 18,095