Investment Securities (Visa Class B Restricted Shares Narrative) (Details 8) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Net Investment Income [Line Items]
Net Gains on Sales of Investment Securities | $	$ 10,430	$ 10,203	$ 10,160
Visa Class B Restricted Securities
Net Investment Income [Line Items]
Conversion ratio to Class A shares	1.6483
Net Gains on Sales of Investment Securities | $	$ 12,100
Sale of investment securities, shares	90,000
Equity securities remaining, shares	86,614
Visa Class A Unrestricted Securities
Net Investment Income [Line Items]
Equity securities remaining, shares	142,766