Segment Information and Major Customers - Disaggregation of Sales by Category (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation Of Revenue [Line Items]
Revenue	$ 154,158	$ 138,081	$ 143,232	$ 127,533	$ 130,129	$ 133,143	$ 128,715	$ 114,523	$ 563,004	$ 506,510	$ 530,061
Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									498,834	438,015	455,226
Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									64,170	68,495	74,835
Access & Aggregation [Member]
Disaggregation Of Revenue [Line Items]
Revenue									344,196	313,138	348,874
Access & Aggregation [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									300,343	262,578	289,980
Access & Aggregation [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									43,853	50,560	58,894
Subscriber Solutions & Experience [Member]
Disaggregation Of Revenue [Line Items]
Revenue									199,621	171,087	152,920
Subscriber Solutions & Experience [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									189,121	161,824	144,651
Subscriber Solutions & Experience [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									10,500	9,263	8,269
Traditional & Other Products [Member]
Disaggregation Of Revenue [Line Items]
Revenue									19,187	22,285	28,267
Traditional & Other Products [Member] | Network Solutions [Member]
Disaggregation Of Revenue [Line Items]
Revenue									9,370	13,613	20,595
Traditional & Other Products [Member] | Services & Support [Member]
Disaggregation Of Revenue [Line Items]
Revenue									$ 9,817	$ 8,672	$ 7,672