Borrowings - Summary of Borrowings from FHLBB (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fixed-rate advances maturing:
2016		$ 23,176
2017	$ 26,932	7,238
2018	4,858	4,500
2019	1,500
2020	3,359
2021	2,018
Advances from FHLBB, Amount	$ 38,667	$ 34,914
Weighted Average Rate
2016		0.52%
2017	0.81%	0.83%
2018	1.07%	1.06%
2019	1.00%
2020	1.55%
2021	1.35%
Advances from FHLBB, Weighted Average Rate	0.94%	0.66%