SEGMENT INFORMATION (REVENUE GEOGRAPHY) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net	$ 461,326	$ 395,507	$ 392,515	$ 394,356	$ 419,133	$ 364,936	$ 349,853	$ 375,249	$ 1,643,704	$ 1,509,171	$ 1,477,365
Property, plant and equipment, gross	801,183				728,009				801,183	728,009	730,028
Other long-term assets	68,969				65,441				68,969	65,441	59,157
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									1,002,524	862,026	820,597
Property, plant and equipment, gross	559,326				508,202				559,326	508,202	490,110
Other long-term assets	57,417				56,459				57,417	56,459	46,029
Philippines [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									370,395	351,829	353,122
Property, plant and equipment, gross	144,213				130,176				144,213	130,176	137,683
Other long-term assets	7,892				5,188				7,892	5,188	7,753
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									100,117	109,104	130,082
Property, plant and equipment, gross	45,743				44,065				45,743	44,065	51,451
Other long-term assets	993				1,329				993	1,329	1,475
Europe Middle East Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									70,613	67,163	62,597
Property, plant and equipment, gross	14,823				10,499				14,823	10,499	10,280
Other long-term assets	993				544				993	544
Other long-term assets by geography											(750)
Asia Pacific India[ Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									55,554	57,978	36,715
Property, plant and equipment, gross	21,562				19,874				21,562	19,874	24,592
Other long-term assets	1,422				1,680				1,422	1,680	4,326
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									44,501	61,071	74,252
Property, plant and equipment, gross	15,516				15,193				15,516	15,193	15,912
Other long-term assets	$ 252				$ 241				$ 252	$ 241	$ 324