SEGMENT INFORMATION (REVENUE GEOGRAPHY) (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, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net	$ 426,623	$ 359,036	$ 353,429	$ 338,277	$ 344,947	$ 312,796	$ 305,105	$ 312,410	$ 1,477,365	$ 1,275,258	$ 1,286,755
Property, plant and equipment, gross	729,979				677,318				729,979	677,318	660,081
Other long-term assets	61,857				47,520				61,857	47,520	42,486
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									820,597	693,023	679,959
Property, plant and equipment, gross	490,110				441,222				490,110	441,222	415,918
Other long-term assets	46,029				36,442				46,029	36,442	34,007
Philippines
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									353,122	351,853	343,013
Property, plant and equipment, gross	137,683				133,214				137,683	133,214	140,712
Other long-term assets	7,753				8,194				7,753	8,194	5,220
Latin America
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									130,082	122,347	147,267
Property, plant and equipment, gross	51,451				50,605				51,451	50,605	49,464
Other long-term assets	1,475				1,161				1,475	1,161	1,161
Canada
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									74,252	13,950	5,780
Property, plant and equipment, gross	15,912				19,988				15,912	19,988	16,239
Other long-term assets	324				514				324	514	1,122
Europe Middle East Africa
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									62,597	65,866	78,182
Property, plant and equipment, gross	10,231				8,805				10,231	8,805	14,567
Other long-term assets	1,950				1,099				1,950	1,099	811
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Sales Revenue Services Net									36,715	28,219	32,554
Property, plant and equipment, gross	24,592				23,484				24,592	23,484	23,181
Other long-term assets	$ 4,326				$ 110				$ 4,326	$ 110	$ 165