Derivatives (Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Thousands		6 Months Ended	12 Months Ended
		Jun. 30, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		$ 2,949,325	$ 2,799,296
Fair Values, Assets		5,760	2,148
Fair Values, Liabilities		1,118	3,938
Less: netting adjustment, Assets	[1]	(16,744)	(4,913)
Less: netting adjustment, Liabilities	[1],[2]	(24,825)	(21,563)
Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		1,358,110	1,358,110
Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		1,591,215	1,441,186
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	[3]	1,227,663	1,144,789
Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		141,907	119,951
Derivatives Not Designated as Hedging Instruments [Member] | Forward Commitments to Sell Residential Mortgage Loans [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		106,970	80,462
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		69,935	53,724
Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		44,740	42,260
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		28,172	19,070
Total derivative assets/liabilities		11,428	14,157
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		28,172	19,070
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets	[3]	25,797	15,408
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		8	23
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		44	1,000
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		555	186
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		1,768	2,453
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2]	50,778	35,952
Total derivative assets/liabilities	[2]	25,953	14,389
Other Liabilities [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2]	22,324	16,495
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2]	28,454	19,457
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2],[3]	25,700	15,857
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2]	56	109
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	[2]	950	290
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	[2]	16	782
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[2]	1,732	2,419
Cash Flow Hedge [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		875,000	875,000
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	[2]	18,321	14,020
Fair Value Hedging [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		483,110	483,110
Fair Values, Liabilities	[2]	$ 4,003	$ 2,475

[1] 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.

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

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