Transfers of Financial Assets - Carrying Amounts of Assets Pledged as Collateral (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Carrying amounts of the assets pledged as collateral
Public deposits	$ 2,800,690	$ 2,521,761
Federal Home Loan Bank	2,388,702	2,097,233
Federal Reserve Bank	914,454	935,672
Repurchase agreements		10,066
ACH transactions	151,526	152,394
Interest rate swaps	27,502	30,399
Total	6,282,874	5,747,525
Securities for reverse repurchase agreements	0	0
Extinguishment of debt
In-substance debt defeasance	$ 0	$ 0

Amount of debt extinguished by in-substance defeasance.

No definition available.

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- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of financial assets which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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- Definition

The carrying amount as of the date of the latest financial statement presented of financial assets which are owned but transferred to serve as collateral for Automated Clearing House (ACH) obligations, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

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No definition available.

+ Details

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- Definition

The carrying amount as of the date of the latest financial statement presented of financial assets which are owned but transferred to serve as collateral for derivative contracts, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable and securities which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable and securities which are owned but transferred to serve as collateral for the payment of Federal Reserve Bank debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for public deposits, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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- References

No definition available.

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- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for repurchase agreements, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 50
-Paragraph 1A
-Subparagraph (b)(1)(i)
-URI http://asc.fasb.org/extlink&oid=64858031&loc=SL6224234-111729

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- References

No definition available.

+ Details

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- Definition

The carrying value of securities purchased to be resold in reverse repurchase transactions as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(2)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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