Investment Securities - Narrative (Details)	3 Months Ended			12 Months Ended
	Mar. 31, 2017 USD ($) purchase_agreement	Dec. 31, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2016 USD ($) purchase_agreement
Investment Securities
Number of inverse putable reverse repurchase of the Bank's secured by collateral | purchase_agreement	3			3
Value of inverse putable reverse repurchases secured by collateral	$ 28,500,000	$ 28,500,000		$ 28,500,000
Other-than-temporary-impairment recovery/(loss) on securities	1,000	0	$ (207,000)
Book value	435,408,000	380,963,000		380,963,000
Accumulated other comprehensive income (loss) before tax amount	(3,000,000)	(4,699,000)		(4,699,000)
Accumulated other comprehensive income, net of tax	(1,708,000)	(2,721,000)		(2,721,000)
Gross gains			762,000
Gross losses	0	0	9,000
Proceeds from sale or maturity of securities available for sale	0	0	186,000,000
FHLB stock	14,400,000
FRB stock	10,900,000
Other stock	12,500,000
Realized OTTI losses		0
HOA
Investment Securities
Value of inverse putable reverse repurchases secured by collateral	22,900,000	21,500,000		21,500,000
Mortgage-backed securities
Investment Securities
Estimated par value of securities pledged as collateral for the Bank's inverse putable reverse repurchases	66,000,000	63,600,000		63,600,000
Fair value of securities pledged as collateral for the Bank's inverse putable reverse repurchases	$ 67,800,000	$ 65,300,000		$ 65,300,000
CRA
Investment Securities
Other-than-temporary-impairment recovery/(loss) on securities			(207,000)
Par value			50
Book value			$ 500,000