SEGMENT INFORMATION (REVENUE GEOGRAPHY) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net	$ 570,974	$ 492,980	$ 453,081	$ 432,213	$ 461,326	$ 395,507	$ 392,515	$ 394,356	$ 1,949,248	$ 1,643,704	$ 1,509,171
Property, plant and equipment, gross	838,306				801,183				838,306	801,183	728,009
Other long-term assets	69,438				68,969				69,438	68,969	65,441
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									1,338,267	1,002,524	862,026
Property, plant and equipment, gross	576,803				559,326				576,803	559,326	508,202
Other long-term assets	55,548				57,417				55,548	57,417	56,459
Philippines [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									347,575	370,395	351,829
Property, plant and equipment, gross	162,391				144,213				162,391	144,213	130,176
Other long-term assets	8,756				7,892				8,756	7,892	5,188
Latin America [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									98,633	100,117	109,104
Property, plant and equipment, gross	46,307				45,743				46,307	45,743	44,065
Other long-term assets	912				993				912	993	1,329
Europe Middle East Africa [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									78,478	70,613	67,163
Property, plant and equipment, gross	23,043				14,823				23,043	14,823	10,499
Other long-term assets	2,328				993				2,328	993	544
Asia Pacific India[ Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									59,750	55,554	57,978
Property, plant and equipment, gross	15,918				21,562				15,918	21,562	19,874
Other long-term assets	1,726				1,422				1,726	1,422	1,680
Canada [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									26,545	44,501	61,071
Property, plant and equipment, gross	13,844				15,516				13,844	15,516	15,193
Other long-term assets	$ 168				$ 252				$ 168	$ 252	$ 241