Summary of Significant Accounting Policies - Components of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue from contracts with customers:
Total revenue from contracts with customers	$ 67,707	$ 69,609	$ 197,552	$ 204,957
Revenue recognized under ASC 842	1,486	1,433	4,779	4,846
Total revenues	69,193	71,042	202,331	209,803
Recurring Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	39,161	37,192	115,196	111,010
Other Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	1,389	1,281	4,099	3,930
Service [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	40,550	38,473	119,295	114,940
Product [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	27,157	31,136	78,257	90,017
Total revenues	$ 28,643	$ 32,569	$ 83,036	$ 94,863