Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Revenue From Contract With Customer [Abstract]
Deferred revenue	$ 2,366	$ 2,833
Deferral of revenue billed in current period, net of recognition	1,658	1,619
Recognition of revenue deferred in prior periods	(1,403)	(1,660)
Deferred revenue	$ 2,621	$ 2,792