Revenues - Revenues from Contracts with Customers Disaggregated by Service Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues	$ 402,925	$ 414,371
Americas [Member]
Disaggregation of Revenue [Line Items]
Revenues	324,777	340,721
Americas [Member] | Customer Engagement Solutions and Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	324,562	340,422
Americas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	215	299
EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenues	78,128	73,627
EMEA [Member] | Customer Engagement Solutions and Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	70,997	71,671
EMEA [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,131	1,956
Other Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	20	23
Other Segment [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 20	$ 23