Interim Consolidated Financial Statements - Summary of Effect of Adopting ASC 606 In Consolidated Statement of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income (loss)	$ (1,733)	$ 3,030
Accounts receivable	7,921	3,839
Deferred commissions	(122)	(235)
Prepaid expenses and other current assets	(5,454)	138
Deferred revenue	17,275	$ 21,538
ASC 606 [Member] | Amounts as if Previous Guidance in Effect [Member]
Cash flows from operating activities:
Net income (loss)	(209)
Accounts receivable	2,249
Deferred commissions	(75)
Prepaid expenses and other current assets	(4,769)
Deferred revenue	$ 20,691