Mortgage Servicing Rights (Amortization method rollforward) (Details 3) - Mortgage Servicing Rights - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Change in Carrying Value of Mortgage Servicing Rights Accounted for Under the Amortization Method, Net of a Valuation Allowance
Balance at beginning of Year	$ 22,008	$ 21,032	$ 22,091
Servicing Rights that Resulted From Asset Transfers	3,976	3,847	1,737
Amortization	(2,816)	(2,892)	(2,832)
Valuation Allowance Provision	0	21	36
Balance at end of Year	23,168	22,008	21,032
Valuation Allowance [Roll Forward]
Balance at Beginning of Year	0	(21)	(57)
Valuation Allowance Provision	0	21	36
Balance at End of Year	0	0	(21)
Fair Value:
Balance at Beginning of Year	25,148	24,804	22,837
Balance at End of Year	$ 26,716	$ 25,148	$ 24,804