Segment Information and Major Customers - Sales and Gross Profit of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Sales	$ 126,836	$ 185,112	$ 184,673	$ 170,279	$ 162,986	$ 168,890	$ 162,701	$ 142,204	$ 666,900	$ 636,781	$ 600,064
Gross Profit	$ 58,815	$ 86,498	$ 84,632	$ 73,715	$ 70,787	$ 75,808	$ 78,955	$ 65,794	303,660	291,344	266,897
Network Solutions [Member]
Segment Reporting Information [Line Items]
Sales									540,396	525,502	527,422
Gross Profit									260,855	254,807	233,579
Services & Support [Member]
Segment Reporting Information [Line Items]
Sales									126,504	111,279	72,642
Gross Profit									$ 42,805	$ 36,537	$ 33,318