Derivative Financial Instruments (Net gains or losses) (Details 3) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains (Losses) Recognized in the Statements of Income	$ 8,362	$ 15,524	$ 6,674
Interest Rate Lock Commitments | Mortgage Banking Income
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains (Losses) Recognized in the Statements of Income	5,643	7,834	2,779
Forward Commitments | Mortgage Banking Income
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains (Losses) Recognized in the Statements of Income	(1,275)	1,741	27
Interest Rate Swap Agreements | Other Noninterest Income
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains (Losses) Recognized in the Statements of Income	698	2,987	1,085
Foreign Exchange Contracts | Other Noninterest Income
Derivative Instruments, Gain (Loss) [Line Items]
Net Gains (Losses) Recognized in the Statements of Income	$ 3,296	$ 2,962	$ 2,783