General - Unaudited Condensed 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	$ 3,254	$ 2,985
Reconciliation of net income to net cash provided by operating activities
Deferred income taxes	1,020	299
Changes in assets and liabilities
Deferred costs	(1,628)	(1,343)
Accrued compensation	(3,939)	(1,870)
Deferred revenue	3,680	5,041
Net cash provided by operating activities	$ 9,349	10,399
ASU 2014-09 [Member] | As Previously Reported [Member]
Cash flows from operating activities
Net income		2,971
Reconciliation of net income to net cash provided by operating activities
Deferred income taxes		310
Changes in assets and liabilities
Deferred costs		(1,649)
Accrued compensation		(1,508)
Deferred revenue		4,988
Net cash provided by operating activities		10,399
ASU 2014-09 [Member] | Adjustments [Member]
Cash flows from operating activities
Net income		14
Reconciliation of net income to net cash provided by operating activities
Deferred income taxes		(11)
Changes in assets and liabilities
Deferred costs		306
Accrued compensation		(362)
Deferred revenue		$ 53