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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Average recorded investment:
Average recorded investment in impaired loans	$ 5,723	$ 7,355	$ 5,858	$ 5,433
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	28	36	91	102
Commercial [Member]
Average recorded investment:
Average recorded investment in impaired loans	2,220	3,035	2,398	1,837
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	14	12	51	49
Commercial Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	2,553	2,767	2,553	2,413
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	3	3	9	9
Residential Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	759	1,538	808	1,172
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	7	20	26	43
Consumer [Member]
Average recorded investment:
Average recorded investment in impaired loans	192	15	99	11
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	$ 4	$ 1	$ 5	$ 1