Derivatives (Effects of Derivative Instruments on the Statements of Income) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ (2,195)	$ 779
Other Noninterest Income [Member] | All Other Instruments [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	809	1,523
Cash Flow Hedge [Member] | Interest Income [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	(2,016)	(618)
Fair Value Hedging [Member] | Interest Expense [Member] | Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative income reflected in income statement	$ (988)	$ (126)