Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Cash flows from operating activities:
Net income	$ 7,788	$ 6,064	$ 6,055	$ 9,094
Accounts receivable			20,020	8,457
Deferred commissions			2,086	1,475
Prepaid expenses and other current assets			280	1,470
Deferred revenue			6,533	$ 9,611
ASC 606 [Member] | Amounts as if Previous Guidance in Effect [Member]
Cash flows from operating activities:
Net income	$ 8,053		7,844
Accounts receivable			16,466
Deferred commissions			1,824
Prepaid expenses and other current assets			1,125
Deferred revenue			$ 7,715