Fair Value Measurements (Beginning And Ending Balances Of Derivative Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2012	Mar. 31, 2011
Derivative [Line Items]
Balance, beginning of period	$ 689	$ 1,090
Cash settlements	(97)	(112)
Realized gains (losses) included in other non-interest income	(22)	(35)
Realized gains (losses) included in other non-interest expense	40	39
Balance, end of period	$ 610	$ 982
Weighted-average risk grade of loans underlying interest rate swaps measured at fair value	11.2
Weighted-average loss severity	22.50%
Minimum [Member]
Derivative [Line Items]
Default on the interest rate swaps, loss severity percentage	10.00%
Maximum [Member]
Derivative [Line Items]
Default on the interest rate swaps, loss severity percentage	50.00%

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain Included in Earnings

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, (Loss) Included in Earnings

+ References

No definition available.

+ Details

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Namespace Prefix:	cfr_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Interest rate swaps, percentage of loss severity on default.

+ References

No definition available.

+ Details

Name:	cfr_InterestRateSwapsPercentageOfLossSeverityOnDefault
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of weighted-average loss severity.

+ References

No definition available.

+ Details

Name:	cfr_PercentageOfWeightedAverageLossSeverity
Namespace Prefix:	cfr_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Weighted-Average Risk Grade Of Loans Underlying Interest Rate Swaps Measured At Fair Value.

+ References

No definition available.

+ Details

Name:	cfr_WeightedAverageRiskGradeOfLoansUnderlyingInterestRateSwapsMeasuredAtFairValue
Namespace Prefix:	cfr_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DerivativeLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents purchases, sales, issuances, and settlements (net) which have taken place during the period in relation to assets measured at fair value on a recurring basis using unobservable inputs (Level 3).

+ References

+ Details

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchasesSalesIssuancesSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

This element represents an asset measured at fair value using significant unobservable inputs (Level 3) which is required for reconciliation purposes of beginning and ending balances.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 157

-Paragraph 32

-Subparagraph c

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6925170&loc=d3e19207-110258

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant