Loans - Schedule of Impaired Loans (Detail) - USD ($) $ in Thousands	3 Months Ended			12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2020
Receivables [Abstract]
Impaired loans without a valuation allowance	$ 6,604	$ 5,172	$ 1,393	$ 5,172
Impaired loans with a valuation allowance	5,532	9,360	4,795	9,360
Total impaired loans	12,136	14,532	6,188	14,532
Valuation allowance related to impaired loans	1,109	1,657	766	1,657
Total non-accrual loans	8,139	9,404	3,344	9,404
Total loans past-due ninety days or more and still accruing		0	0	0
Average investment in impaired loans	$ 13,467	$ 14,868	$ 4,314	$ 10,234