Fair Value Disclosures Related to Grants, Exercises and Vested Options (Detail) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Proceeds from stock options exercised		$ 66	$ 0	$ 66	$ 0
Intrinsic value of stock options exercised	[1]	$ 42	$ 0	$ 42	$ 0
Weighted-average fair value of options granted during period		$ 0.49	$ 0	$ 0.72	$ 0.29
Total fair value of stock options vested during the period		$ 8	$ 34	$ 395	$ 188

[1] The intrinsic value of stock options exercised is the amount by which the market price of the stock on the date of exercise exceeded the exercise price of the options.