Fair Value of Financial Instruments - Assets measured at fair value on nonrecurring basis (Details) - Non-recurring - Level III - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Impaired loans
Quantitative information about assets measured at fair value on a non-recurring basis
Fair Value	$ 11,989	$ 14,091
Impaired loans | Appraisal of collateral | Minimum
Fair Value Inputs [Abstract]
Appraisal adjustments (as a percent)	20.00%	20.00%
Liquidation expenses (as a percent)	5.00%	5.00%
Impaired loans | Appraisal of collateral | Maximum
Fair Value Inputs [Abstract]
Appraisal adjustments (as a percent)	30.00%	30.00%
Liquidation expenses (as a percent)	10.00%	10.00%
Other real estate owned
Quantitative information about assets measured at fair value on a non-recurring basis
Fair Value	$ 274	$ 575
Other real estate owned | Appraisal of collateral | Minimum
Fair Value Inputs [Abstract]
Appraisal adjustments (as a percent)	20.00%	20.00%
Liquidation expenses (as a percent)	5.00%	5.00%
Other real estate owned | Appraisal of collateral | Maximum
Fair Value Inputs [Abstract]
Appraisal adjustments (as a percent)	30.00%	30.00%
Liquidation expenses (as a percent)	10.00%	10.00%
Mortgage servicing rights
Quantitative information about assets measured at fair value on a non-recurring basis
Fair Value	$ 1,155	$ 1,423
Mortgage servicing rights | Discounted cash flow
Fair Value Inputs [Abstract]
Prepayment rate (as a percent)	12.00%	12.00%
Cost of service (as a percent)	0.25%	0.25%
Discount rate (as a percent)	12.00%	12.00%