Derivative Financial Instruments (Narrative) (Details)	12 Months Ended
	Dec. 31, 2017 USD ($) derivative_instruments	Dec. 31, 2016 USD ($) derivative_instruments
Derivative Instruments, Gain (Loss) [Line Items]
Amount reclassified from accumulated other comprehensive income to interest expense in next twelve months	$ 5,500,000
Fair value of interest rate derivatives in a net liability position	1,500,000
Forward commitments to sell mortgage loans
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	551,900,000	$ 773,400,000
Interest Rate Lock Commitments
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	250,300,000
Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 37,600,000
Covered call options
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives, number of instruments held | derivative_instruments	0	0
Designated as hedging instrument | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 1,125,000,000
Designated as hedging instrument | Cash flow hedging | Interest rate swap | Cash flow hedge of variable rate deposits
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instruments	6
Designated as hedging instrument | Cash flow hedging | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Hedge ineffectiveness recognized	$ 0	$ 0
Designated as hedging instrument | Fair value hedging | Interest rate swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of interest rate derivatives held | derivative_instruments	11
Notional Amount	$ 125,800,000
Designated as hedging instrument | Fair value hedging | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Fair value of derivatives, hedge ineffectiveness	27,000	$ 12,000
Not designed as hedging instrument | Interest Rate Contract
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 5,100,000,000