Segment Information and Major Customers - Sales and Gross Profit of Reportable Segments (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Revenue	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 115,787	$ 114,092	$ 156,391	$ 143,791	$ 506,510	$ 530,061	$ 529,277
Gross Profit	$ 53,517	$ 58,962	$ 53,472	$ 51,600	$ 47,209	$ 46,331	$ 65,015	$ 60,612	217,551	219,167	203,565
Network Solutions [Member]
Segment Reporting Information [Line Items]
Revenue									438,015	455,226	458,232
Gross Profit									193,789	191,549	179,303
Services & Support [Member]
Segment Reporting Information [Line Items]
Revenue									68,495	74,835	71,045
Gross Profit									$ 23,762	$ 27,618	$ 24,262