Restricted Shares Issued in Conjunction with Stock Plan (Detail) - Restricted Stock $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) shares
Period 1
Class of Stock [Line Items]
Issuance Date	Jan. 29, 2018
Shares | shares	37,510
Aggregate Market Value | $	$ 1.6
Period 2
Class of Stock [Line Items]
Issuance Date	Jan. 29, 2019
Shares | shares	33,150
Aggregate Market Value | $	$ 1.6
Period 3
Class of Stock [Line Items]
Issuance Date	Jan. 28, 2020
Shares | shares	28,630
Aggregate Market Value | $	$ 1.8
Period 4
Class of Stock [Line Items]
Issuance Date	Jul. 28, 2020
Shares | shares	3,000
Aggregate Market Value | $	$ 0.1