Changes in Deferred Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue From Contract With Customer [Abstract]
Deferred revenue	$ 2,366	$ 2,833
Deferral of revenue billed in current period, net of recognition	392	384
Recognition of revenue deferred in prior periods	(793)	(931)
Deferred revenue	$ 1,965	$ 2,286