Loans - Schedule of Average Recorded Investment in Impaired Loans and Related Interest Income Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Average recorded investment:
Average recorded investment in impaired loans	$ 6,113	$ 5,864
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	50	30
Commercial [Member]
Average recorded investment:
Average recorded investment in impaired loans	2,025	2,453
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	10	18
Commercial Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	3,139	2,556
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	30	2
Residential Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	810	846
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	8	10
Consumer [Member]
Average recorded investment:
Average recorded investment in impaired loans	139	$ 9
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	$ 2