SEGMENT AND GEOGRAPHICAL REPORTING, Geographical Information (Details) - USD ($) $ in Thousands	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Revenues	$ 265,700	$ 251,900	$ 250,700	$ 238,500	$ 222,300	$ 230,000	$ 256,200	$ 253,600	$ 278,600	$ 303,100	$ 323,700	$ 341,600	$ 1,006,782	$ 962,092	$ 1,247,043
Property and equipment, net	53,337				60,807								53,337	60,807
Reportable Geographical Components [Member] | United States [Member]
Segment Reporting Information [Line Items]
Revenues													902,636	873,926	1,119,210
Property and equipment, net	42,683				48,635								42,683	48,635
Reportable Geographical Components [Member] | Canada [Member]
Segment Reporting Information [Line Items]
Revenues													104,146	88,166	$ 127,833
Property and equipment, net	$ 10,654				$ 12,172								$ 10,654	$ 12,172