Loans - Schedule of Average Recorded Investment in Impaired Loans and Related Interest Income Recognized (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Average recorded investment:
Average recorded investment in impaired loans	$ 5,021	$ 7,934	$ 6,373	$ 7,038
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	26	34	55	63
Commercial [Member]
Average recorded investment:
Average recorded investment in impaired loans	1,190	2,794	1,491	3,505
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	10	17	21	31
Commercial Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	2,700	3,600	3,595	2,019
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	4	2	8	2
Residential Real Estate [Member]
Average recorded investment:
Average recorded investment in impaired loans	1,131	1,540	1,287	1,514
Interest income recognized:
Interest income recognized on a cash basis on impaired loans	$ 12	$ 15	$ 26	$ 30