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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Average recorded investment:
Average recorded investment in impaired loans	$ 9,166	$ 8,509	$ 7,781	$ 8,696
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	30	72	93	229
Commercial [Member]
Average recorded investment:
Average recorded investment in impaired loans	3,084	6,389	3,376	6,393
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	10	54	41	176
Commercial Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	4,712	660	2,934	799
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	7	3	9	9
Residential Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	1,370	1,460	1,471	1,504
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	$ 13	$ 15	$ 43	$ 44