Segments and Geographic Information - Revenues by Segment from Major Customers Other than AT&T Corporation (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
Greater Than Ten Percent of Segment Revenue Other Than AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Amount	68,720	79,811	55,123
EMEA [Member] | Greater Than Ten Percent of Segment Revenue Other Than AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
Amount	$ 68,720	$ 79,811	$ 55,123
Sales Revenue, Net [Member] | Greater Than Ten Percent of Segment Revenue Other Than AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
% of Revenues	5.30%	6.00%	4.40%
Sales Revenue, Net [Member] | Americas [Member] | Greater Than Ten Percent of Segment Revenue Other Than AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
% of Revenues	0.00%	0.00%	0.00%
Sales Revenue, Net [Member] | EMEA [Member] | Greater Than Ten Percent of Segment Revenue Other Than AT&T Corporation [Member] | Customer Concentration Risk [Member]
Revenue, Major Customer [Line Items]
% of Revenues	28.50%	31.10%	25.90%