Derivatives (Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		$ 3,141,363	$ 3,024,565
Fair Values, Assets		1,726	3,325
Fair Values, Liabilities		4,598	2,160
Less: netting adjustment, Assets	[1],[2]	(13,514)	(11,979)
Less: netting adjustment, Liabilities	[1],[2]	(26,407)	(22,588)
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		1,363,110	1,358,110
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		1,778,253	1,666,455
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	[3]	1,373,378	1,277,404
Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		169,317	171,222
Derivatives Not Designated as Hedging Instruments [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		82,845	77,208
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		69,931	59,119
Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		39,029	37,749
Derivatives Not Designated as Hedging Instruments [Member] | Visa Class B derivative contract [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		43,753	43,753
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	39,341	28,959
Total derivative assets/liabilities	[1]	25,827	16,980
Other Assets [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	9,765	3,954
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	29,576	25,005
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1],[3]	28,570	23,670
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	10	10
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	21	110
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	493	464
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	482	751
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	44,536	44,815
Total derivative assets/liabilities	[1]	18,129	22,227
Other Liabilities [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	5,859	11,262
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	38,677	33,553
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1],[3]	30,506	24,669
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	162	131
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	607	664
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate-Lock Commitments on Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	1	67
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	448	718
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Visa Class B derivative contract [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	6,953	7,304
Cash Flow Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		975,000	875,000
Cash Flow Hedge [Member] | Other Assets [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[1]	9,765	3,954
Cash Flow Hedge [Member] | Other Liabilities [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	4,899	9,173
Fair Value Hedging [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		388,110	483,110
Fair Value Hedging [Member] | Other Liabilities [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[1]	$ 960	$ 2,089

[1] Derivative assets and liabilities are reported at fair value in other assets or other liabilities, respectively, in the consolidated balance sheets.

[2] Represents balance sheet netting of derivative assets and liabilities for variation margin collateral held or placed with the same central clearing counterparty.  See offsetting assets and liabilities for further information.

[3] The notional amount represents both the customer accommodation agreements and offsetting agreements with unrelated financial institutions