Segment Information and Major Customers - Sales Information by Product Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue from External Customer [Line Items]
Sales	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 139,013	$ 158,078	$ 160,138	$ 142,835	$ 636,781	$ 600,064	$ 630,007
Access & Aggregation [Member]
Revenue from External Customer [Line Items]
Sales									436,372	405,698	401,769
Customer Devices [Member]
Revenue from External Customer [Line Items]
Sales									137,608	125,565	138,051
Traditional & Other Products [Member]
Revenue from External Customer [Line Items]
Sales									$ 62,801	$ 68,801	$ 90,187