Fair Market Value of Financial Assets and Liabilities, Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Mortgage Servicing Rights [Member] | Discount Cash Flows, Computer Pricing Model [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 3,706	$ 3,484
Mortgage Servicing Rights [Member] | Discount Cash Flows, Computer Pricing Model [Member] | Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member]
Unobservable inputs [Abstract]
Constant prepayment rate	7.00%	7.00%
Probability of default	0.00%	0.00%
Discount rate	10.00%	10.00%
Mortgage Servicing Rights [Member] | Discount Cash Flows, Computer Pricing Model [Member] | Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member]
Unobservable inputs [Abstract]
Constant prepayment rate	33.00%	45.00%
Probability of default	100.00%	100.00%
Discount rate	11.50%	11.50%
Mortgage Servicing Rights [Member] | Discount Cash Flows, Computer Pricing Model [Member] | Significant Unobservable Inputs (Level 3) [Member] | Weighted Average [Member]
Unobservable inputs [Abstract]
Constant prepayment rate	8.90%	10.00%
Probability of default	3.30%	3.00%
Discount rate	10.10%	10.10%
Impaired Loans (Collateral Dependent) [Member] | Market Comparable Properties [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 654	$ 2,709
Impaired Loans (Collateral Dependent) [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member]
Unobservable inputs [Abstract]
Marketability discount	10.00%	1.90%
Impaired Loans (Collateral Dependent) [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member]
Unobservable inputs [Abstract]
Marketability discount	91.30%	89.80%
Impaired Loans (Collateral Dependent) [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Weighted Average [Member]
Unobservable inputs [Abstract]
Marketability discount	37.10%	38.50%
Other Real Estate Owned [Member] | Market Comparable Properties [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value	$ 2,243	$ 18,951
Other Real Estate Owned [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Minimum [Member]
Unobservable inputs [Abstract]
Comparability adjustments	1.00%	6.00%
Other Real Estate Owned [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Maximum [Member]
Unobservable inputs [Abstract]
Comparability adjustments	39.60%	58.60%
Other Real Estate Owned [Member] | Market Comparable Properties [Member] | Significant Unobservable Inputs (Level 3) [Member] | Weighted Average [Member]
Unobservable inputs [Abstract]
Comparability adjustments	14.50%	15.00%