Retirement Plan (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Employers' sponsors contribution retirement plan	90.00%
Contribution to retirement plan, percentage of employee contribution	100.00%
Percentage of employee contribution to retirement plan	5.00%
Employers' sponsors contribution retirement plan amount	$ 1.1	$ 1.0	$ 0.8