Summary of Significant Accounting Principles - Components of Revenue from Contracts with Customers (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Revenue from contracts with customers:
Total revenue from contracts with customers	$ 69,644	$ 56,957	$ 135,348	$ 108,878
Product revenue recognized under ASC 840	1,144		3,413
Total revenues	70,788	56,957	138,761	108,878
Recurring Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	37,094	30,066	73,818	58,011
Other Service Revenues [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	1,381	1,011	2,649	2,578
Service Revenue [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	38,475	31,077	76,467	60,589
Product [Member]
Revenue from contracts with customers:
Total revenue from contracts with customers	31,169	25,880	58,881	48,289
Total revenues	$ 32,313	$ 25,880	$ 62,294	$ 48,289