Investment Securities - Narrative (Details)	3 Months Ended				9 Months Ended
	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) purchase_agreement	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Investment Securities
Number of inverse putable reverse repurchase of the Bank's secured by collateral | purchase_agreement					3
Value of inverse putable reverse repurchases secured by collateral	$ 28,500,000				$ 28,500,000
Realized OTTI losses		$ 0		$ 0		$ 0
Other-than-temporary-impairment recovery/(loss) on investment securities	2,000	0		0	(205,000)	0
Book value	313,200,000				313,200,000		$ 280,273,000
Gross gains	512,000	532,000		52,000	1,800,000	316,000
Gross losses	0	0		14,000	9,000	23,000
Proceeds from sale or maturity of securities available for sale	16,600,000	$ 21,000,000		$ 10,400,000	223,000,000	26,500,000
Accumulated other comprehensive income (loss) before tax amount	2,300,000				2,300,000		562,000
Accumulated other comprehensive income, net of tax	1,363,000				1,363,000		$ 332,000
FHLB stock	14,400,000				14,400,000
FRB stock	10,900,000				10,900,000
Other stock	4,700,000				4,700,000
Proceeds from sale or maturity of securities available for sale					229,855,000	$ 26,520,000
HOA
Investment Securities
Value of inverse putable reverse repurchases secured by collateral	17,700,000				17,700,000
Mortgage-backed securities
Investment Securities
Estimated par value of securities pledged as collateral for the Bank's inverse putable reverse repurchases	61,100,000				61,100,000
Fair value of securities pledged as collateral for the Bank's inverse putable reverse repurchases	$ 63,800,000				$ 63,800,000
CRA
Investment Securities
Other-than-temporary-impairment recovery/(loss) on investment securities			$ (207,000)
Par value			50
Book value			$ 500,000