Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue From Contract With Customer [Abstract]
Deferred revenue	$ 2,833	$ 2,810
Deferral of revenue billed in current period, net of recognition	1,591	2,149
Recognition of revenue deferred in prior periods	(2,058)	(2,126)
Deferred revenue	$ 2,366	$ 2,833