Revenues - Revenues from Contracts with Customers Disaggregated by Service Type (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 411,166	$ 402,925
% of Revenues	100.00%	100.00%
Americas [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 332,926	$ 324,777
% of Revenues	81.00%	80.60%
Americas [Member] | Customer Engagement Solutions and Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 332,614	$ 324,562
% of Revenues	80.90%	80.60%
Americas [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 312	$ 215
% of Revenues	0.10%	0.00%
EMEA [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 78,233	$ 78,128
% of Revenues	19.00%	19.40%
EMEA [Member] | Customer Engagement Solutions and Services [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 72,633	$ 70,997
% of Revenues	17.70%	17.60%
EMEA [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 5,600	$ 7,131
% of Revenues	1.30%	1.80%
Other Segment [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 7	$ 20
% of Revenues	0.00%	0.00%
Other Segment [Member] | Other Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 7	$ 20
% of Revenues	0.00%	0.00%