Derivatives (Fair Values of Derivative Financial Instruments) (Details) - USD ($) $ in Thousands		3 Months Ended		12 Months Ended
		Mar. 31, 2018		Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		$ 2,849,743		$ 2,799,296
Fair Values, Assets		4,508		2,148
Fair Values, Liabilities		1,584		3,938
Less: netting adjustment, Assets	[1]	(14,081)		(4,913)
Less: netting adjustment, Liabilities	[1]	(19,162)	[2]	(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		1,491,633		1,441,186
Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount	[3]	1,184,109		1,144,789
Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		121,479		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		81,326		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		61,904		53,724
Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Notional or Contractual Amount		42,815		42,260
Other Assets [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		26,764		19,070
Total derivative assets/liabilities		12,683		14,157
Other Assets [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		1,752
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		25,012		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]	20,680		15,408
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		13		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		847		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		376		186
Other Assets [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		3,096		2,453
Other Liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities		41,691	[2]	35,952
Total derivative assets/liabilities		22,529	[2]	14,389
Other Liabilities [Member] | Derivatives Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities		16,615	[2]	16,495
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities		25,076	[2]	19,457
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities	[3]	20,710	[2]	15,857
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Risk Participation Agreements [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities		61	[2]	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		454	[2]	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		789	[2]	782
Other Liabilities [Member] | Derivatives Not Designated as Hedging Instruments [Member] | Foreign Exchange Forward Contracts [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Liabilities		3,062	[2]	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 Assets [Member] | Derivatives Designated as Hedging Instruments [Member] | Interest Rate Swaps [Member]
Derivatives, Fair Value [Line Items]
Fair Values, Assets		1,752
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		12,667	[2]	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		$ 3,948	[2]	$ 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] March 31, 2018December 31, 2017Derivative (1)Derivative (1)(in thousands)Type of HedgeNotional or Contractual AmountAssetsLiabilitiesNotional or Contractual AmountAssetsLiabilitiesDerivatives designated as hedging instruments:Interest rate swapsCash Flow$ 875,000 $ 1,752 $ 12,667 $ 875,000 $ -$ 14,020 Interest rate swapsFair Value 483,110 - 3,948 483,110 - 2,475 $ 1,358,110 $ 1,752 $ 16,615 $ 1,358,110 $ -$ 16,495 Derivatives not designated as hedging instruments:Interest rate swaps (2)N/A$ 1,184,109 $ 20,680 $ 20,710 $ 1,144,789 $ 15,408 $ 15,857 Risk participation agreementsN/A 121,479 13 61 119,951 23 109 Forward commitments to sell residential mortgage loansN/A 81,326 847 454 80,462 1,000 290 Interest rate-lock commitments on residential mortgage loansN/A 61,904 376 789 53,724 186 782 Foreign exchange forward contractsN/A 42,815 3,096 3,062 42,260 2,453 2,419 1,491,633 25,012 25,076 1,441,186 19,070 19,457 Total derivatives$ 2,849,743 $ 26,764 $ 41,691 $ 2,799,296 $ 19,070 $ 35,952 Less: netting adjustment (3) (14,081) (19,162) (4,913) (21,563)Total derivative assets/liabilities$ 12,683 $ 22,529 $ 14,157 $ 14,389 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.