Loans And Allowance For Credit Losses (Schedule Of Outstanding Balances Of All Required Payments And The Related Carrying Amounts For PCI Loans) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Loans And Allowance For Credit Losses [Abstract]
Commercial	$ 96,157	$ 104,942
Commercial real estate	105,234	118,217
Consumer	17,129	17,910
Outstanding balance	218,520	241,069
Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net	162,890	179,299
ALLL	1,438	2,800
Carrying amount, net	$ 161,452	$ 176,499

Loans And Allowance For Credit Losses (Schedule Of Outstanding Balances Of All Required Payments And The Related Carrying Amounts For PCI Loans) (Details) (USD $)
In Thousands, unless otherwise specified

Mar. 31, 2015

Dec. 31, 2014

Loans And Allowance For Credit Losses [Abstract]

Commercial

$ 96,157us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCommercialOutstandingBalance

$ 104,942us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCommercialOutstandingBalance

Commercial real estate

105,234zion_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCommercialRealEstate

118,217zion_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCommercialRealEstate

Consumer

17,129us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesConsumerOutstandingBalance

17,910us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesConsumerOutstandingBalance

Outstanding balance

218,520us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance

241,069us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesOutstandingBalance

Certain Loans Acquired in Transfer Accounted for as Debt Securities, Carrying Amount, Net

162,890us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet

179,299us-gaap_CertainLoansAcquiredInTransferAccountedForAsDebtSecuritiesCarryingAmountNet

ALLL

1,438us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAllowanceForLoanLosses

2,800us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesAllowanceForLoanLosses

Carrying amount, net

$ 161,452us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet

$ 176,499us-gaap_CertainLoansAcquiredInTransferNotAccountedForAsDebtSecuritiesCarryingAmountNet

- Definition

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and other-than-temporary impairments), for loans accounted for as debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

+ Details

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- Definition

Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows previously expected. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 15

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=27045933&loc=d3e13503-111538

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 30

-Section 50

-Paragraph 2

-Subparagraph (b)(2)

-URI http://asc.fasb.org/extlink&oid=6379141&loc=d3e15032-111544

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- Definition

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

+ Details

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- Definition

The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to commercial loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

+ Details

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- Definition

The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to consumer loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

+ Details

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- Definition

The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

+ References

+ Details

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- Definition

Certain loans acquired in transfer not accounted for as debt securities commercial real estate.

+ References

No definition available.

+ Details

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