Summary of Significant Accounting Policies - Components of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue from contracts with customers:
Total revenue from contracts with customers									$ 266,254	$ 270,607	$ 247,880
Product sales recognized under ASC 842									5,759	5,533	6,340
Total revenues	$ 69,682	$ 69,193	$ 67,103	$ 66,035	$ 66,337	$ 71,042	$ 70,788	$ 67,973	272,013	276,140	254,220
Recurring Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers									155,284	148,367	126,540
Other Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers									5,310	5,222	8,398
Service [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers									160,594	153,589	134,938
Product [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers									105,660	117,018	112,942
Total revenues									$ 111,419	$ 122,551	$ 119,282