Segments and Geographic Information - Revenues by Segment from Major Customers (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenue, Major Customer [Line Items]
Amount	$ 1,286,340	$ 1,327,523	$ 1,263,460
AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Amount	220,452	216,126	166,401
AT&T Corporation [Member] | Customer Concentration Risk [Member] | Americas [Member]
Revenue, Major Customer [Line Items]
Amount	217,449	212,607	162,888
AT&T Corporation [Member] | Customer Concentration Risk [Member] | EMEA [Member]
Revenue, Major Customer [Line Items]
Amount	$ 3,003	$ 3,519	$ 3,513
AT&T Corporation [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Revenue, Major Customer [Line Items]
% of Revenues	17.10%	16.30%	13.20%
AT&T Corporation [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | Americas [Member]
Revenue, Major Customer [Line Items]
% of Revenues	20.80%	19.90%	15.50%
AT&T Corporation [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member] | EMEA [Member]
Revenue, Major Customer [Line Items]
% of Revenues	1.20%	1.40%	1.70%