Derivative Instruments and Balance Sheet Offsetting (Notional Amount and Fair Value) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Notional Amount	$ 3,516,418	$ 2,210,925
Gross Derivative Assets	38,595	18,681
Gross Derivative Liabilities	32,379	12,357
Credit valuation adjustments for counterparty credit risk	900	800
Designated as hedging
Derivative [Line Items]
Notional Amount	820,000	620,000
Gross Derivative Assets	10,148	5,899
Gross Derivative Liabilities	3,278	0
Designated as hedging | Interest rate swaps
Derivative [Line Items]
Notional Amount	820,000	620,000
Gross Derivative Assets	10,148	5,899
Gross Derivative Liabilities	3,278	0
Not designated as hedging
Derivative [Line Items]
Notional Amount	2,696,418	1,590,925
Gross Derivative Assets	28,447	12,782
Gross Derivative Liabilities	29,101	12,357
Not designated as hedging | Customer-initiated derivatives
Derivative [Line Items]
Notional Amount	2,477,640	1,365,119
Gross Derivative Assets	26,680	9,376
Gross Derivative Liabilities	27,664	10,139
Not designated as hedging | Foreign exchange forwards
Derivative [Line Items]
Notional Amount	0	0
Gross Derivative Assets	0	0
Gross Derivative Liabilities	0	0
Not designated as hedging | Forward contracts related to mortgage loans to be delivered for sale
Derivative [Line Items]
Notional Amount	127,159	115,996
Gross Derivative Assets	0	0
Gross Derivative Liabilities	719	34
Not designated as hedging | Interest rate lock commitments
Derivative [Line Items]
Notional Amount	54,848	71,003
Gross Derivative Assets	1,049	1,222
Gross Derivative Liabilities	0	0
Not designated as hedging | Power Equity CD
Derivative [Line Items]
Notional Amount	36,771	38,807
Gross Derivative Assets	718	2,184
Gross Derivative Liabilities	$ 718	$ 2,184