Other Borrowed Funds and Subordinated Debentures - Schedule of the Maturity Distribution of FHLBB Advances with the Weighted Average Interest Rates (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Federal Home Loan Bank, Advances, Fiscal Year Maturity [Abstract]
Within one year	$ 77,500	$ 100,000	$ 169,500
Over one year to two years	54,500	57,500	55,000
Over two years to three years	58,000	54,500	45,000
Over three years to five years	58,000	91,000	70,000
Over five years	45,000	65,000	56,000
Federal Home Loan Bank, Advances, Total	$ 293,000	$ 368,000	$ 395,500
Within one year, Weighted Average Rate	2.21%	1.89%	0.51%
Over one year to two years, Weighted Average Rate	2.25%	2.72%	3.07%
Over two years to three years, Weighted Average Rate	1.87%	2.25%	3.18%
Over three years to five years, Weighted Average Rate	2.68%	1.85%	2.43%
Over five years, Weighted Average Rate	2.85%	3.23%	3.16%
Weighted Average Rate, Total	2.34%	2.30%	1.89%