Summary of Significant Accounting Policies - Schedule of Revenue Disaggregated by Revenue Type, Geographic Region and Customer (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation Of Revenue [Line Items]
Total revenue	$ 253,119	$ 245,617
Percentage of total revenue	100.00%	100.00%
Broadband/Cable/Satellite
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	57.00%	58.00%
Telecommunications
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	18.00%	17.00%
Other
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	25.00%	25.00%
Americas (principally the U.S.)
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	86.00%	88.00%
Europe, Middle East and Africa
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	10.00%	9.00%
Asia Pacific
Disaggregation Of Revenue [Line Items]
Percentage of total revenue	4.00%	3.00%
Cloud and Related Solutions
Disaggregation Of Revenue [Line Items]
Total revenue	$ 227,019	$ 222,220
Software and Services
Disaggregation Of Revenue [Line Items]
Total revenue	14,779	13,206
Maintenance
Disaggregation Of Revenue [Line Items]
Total revenue	$ 11,321	$ 10,191