Loans - Schedule of Average Recorded Investment in Impaired Loans and Related Interest Income Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Average recorded investment:
Average recorded investment in impaired loans	$ 4,386	$ 5,724	$ 5,258	$ 5,858
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	32	28	122	91
Commercial [Member]
Average recorded investment:
Average recorded investment in impaired loans	1,237	2,220	1,745	2,398
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	3	14	22	51
Commercial Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	2,199	2,553	2,557	2,553
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	20	3	71	9
Residential Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	822	759	822	808
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	7	7	23	26
Consumer [Member]
Average recorded investment:
Average recorded investment in impaired loans	128	192	134	99
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	$ 2	$ 4	$ 6	$ 5