Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net income	$ 3,950	$ 3,953	$ 10,005	$ 13,047
Accounts receivable			31,857	20,140
Deferred commissions			3,716	2,906
Prepaid expenses and other current assets			(68)	(979)
Deferred revenue			(8,205)	$ (3,473)
ASC 606 [Member] | Amounts as if Previous Guidance in Effect [Member]
Cash flows from operating activities:
Net income	$ 3,136		10,980
Accounts receivable			28,572
Deferred commissions			3,447
Prepaid expenses and other current assets			714
Deferred revenue			$ (6,408)