Summary of Significant Accounting Policies - Components of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from contracts with customers:
Total revenue from contracts with customers	$ 64,829	$ 65,704
Revenue recognized under ASC 842	1,206	2,269
Total revenues	66,035	67,973
Recurring Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	37,529	36,725
Other Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	1,478	1,267
Service [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	39,007	37,992
Product [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	25,822	27,712
Total revenues	$ 27,028	$ 29,981