Estimated Fair Values (Assets And Liabilities Carried At Fair Value On A Nonrecurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other real estate remeasured during current year	$ 43,601		$ 51,097	$ 53,988		$ 61,231
Mortgage servicing rights	21,633	$ 21,657	21,945	$ 22,003	$ 20,524	$ 20,415
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	107,614		72,539
Other real estate remeasured during current year	27,027		40,167
Fair Value, Measurements, Nonrecurring | Quoted Prices in Active Markets for Identical Assets and Liabilities (Level 1 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate remeasured during current year	0		0
Fair Value, Measurements, Nonrecurring | Quoted Prices for Similar Assets and Liabilities (Level 2 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	0		0
Other real estate remeasured during current year	0		0
Fair Value, Measurements, Nonrecurring | Significant Unobservable Inputs (Level 3 Inputs)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impaired loans	107,614		72,539
Other real estate remeasured during current year	$ 27,027		$ 40,167