Summary of Significant Accounting Principles - Components of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Revenue from contracts with customers:
Service revenues	$ 37,992	$ 29,512
Product revenue	27,712	22,409
Total revenue from contracts with customers	65,704	51,921
Revenue recognized under ASC 840	2,269
Total revenues	67,973	51,921
Recurring Service Revenues [Member]
Revenue from contracts with customers:
Service revenues	36,725	27,945
Other Service Revenues [Member]
Revenue from contracts with customers:
Service revenues	$ 1,267	$ 1,567