Fair Value Disclosures, Quantitative Information About Level 3 (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Significant Un-observable Inputs (Level 3) [Member]
Asset (Liability) Fair Value [Abstract]
Capitalized mortgage loan servicing rights	$ 17,783,000	$ 15,699,000
Impaired loan [Abstract]
Commercial	1,179,000	1,334,000
Mortgage	276,000	546,000
Other real estate [Abstract]
Mortgage	$ 171,000	$ 251,000
Present Value of Net Servicing Revenue [Member] | Minimum [Member]
Unobservable Inputs Weighted Average [Abstract]
Discount rate	10.00%	9.88%
Cost to service	$ 66	$ 66
Ancillary income	$ 20	$ 20
Float rate	2.70%	2.24%
Present Value of Net Servicing Revenue [Member] | Maximum [Member]
Unobservable Inputs Weighted Average [Abstract]
Discount rate	13.00%	11.00%
Cost to service	$ 216	$ 216
Ancillary income	$ 36	$ 36
Float rate	2.70%	2.24%
Present Value of Net Servicing Revenue [Member] | Weighted Average [Member]
Unobservable Inputs Weighted Average [Abstract]
Discount rate	10.14%	10.11%
Cost to service	$ 81	$ 81
Ancillary income	$ 23	$ 23
Float rate	2.70%	2.24%
Sales Comparison Approach [Member] | Impaired Loans Commercial [Member] | Minimum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	(32.50%)	(32.50%)
Sales Comparison Approach [Member] | Impaired Loans Commercial [Member] | Maximum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	25.00%	25.00%
Sales Comparison Approach [Member] | Impaired Loans Commercial [Member] | Weighted Average [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	(3.90%)	(4.50%)
Sales Comparison Approach [Member] | Impaired Loans Mortgage [Member] | Minimum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	(30.90%)	(21.10%)
Sales Comparison Approach [Member] | Impaired Loans Mortgage [Member] | Maximum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	77.90%	34.10%
Sales Comparison Approach [Member] | Impaired Loans Mortgage [Member] | Weighted Average [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	7.00%	(2.70%)
Sales Comparison Approach [Member] | Other Real Estate Mortgage [Member] | Minimum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	(33.00%)	(33.00%)
Sales Comparison Approach [Member] | Other Real Estate Mortgage [Member] | Maximum [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	44.50%	44.50%
Sales Comparison Approach [Member] | Other Real Estate Mortgage [Member] | Weighted Average [Member]
Unobservable Inputs Weighted Average [Abstract]
Adjustment for differences between comparable sales	(2.00%)	(1.00%)