Segment Information - Sales Information by Category (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue from External Customer [Line Items]
Sales	$ 142,204	$ 142,835
Access & Aggregation [Member]
Revenue from External Customer [Line Items]
Sales	93,855	92,851
Customer Devices [Member]
Revenue from External Customer [Line Items]
Sales	32,353	31,704
Traditional & Other Products [Member]
Revenue from External Customer [Line Items]
Sales	$ 15,996	$ 18,280