Contingencies - Additional Information (Details) $ in Millions	3 Months Ended
Mar. 31, 2017 USD ($) Lawsuit	Mar. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Unused commitments to extend credit	$ 3,052.0	$ 3,007.0
Pending or Threatened Litigation, Stanford Financial Group [Member]
Legal Proceedings [Abstract]
Lawsuits naming entity as defendant, number \| Lawsuit	3
Standby Letters of Credit [Member]
Loss Contingencies [Line Items]
Letters of credit, maturity term - maximum	3 years
Collateral held, fair value	$ 33.7	30.0
Standby Letters of Credit [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Potential exposure to credit loss in the event of nonperformance	$ 109.2	$ 114.9

Legal Proceedings [Abstract]

No definition available.

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- Definition

The maximum maturity (in years) of outstanding letters of credit issued by company.

+ References

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

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- Definition

Number of pending claims pertaining to a loss contingency.

+ References

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- Definition

The carrying amount (fair value) as of the balance sheet date of securities held that had been pledged by counterparties under financing and lending arrangements, pursuant to which the entity has the right by agreement or custom to sell or re-pledge such securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=66008989&loc=d3e5086-111524

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- Definition

Unused amount of commitments to extend credit to customers.

+ References

No definition available.

+ Details

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