Securities (Securities, with Unrealized Losses Segregated by Length of Impairment) (Details) (USD $) In Thousands	Jun. 30, 2011
Held To Maturity, Less than 12 Months, Estimated Fair Value	$ 23,446
Held To Maturity, More than 12 Months, Estimated Fair Value
Held To Maturity, Total Estimated Fair Value	23,446
Held To Maturity, Less than 12 Months, Unrealized Losses	345
Held To Maturity, More than 12 Months, Unrealized Losses
Held To Maturity, Total Unrealized Losses	345
Available for Sale, Less than 12 months, Estimated Fair Value	272,158
Available for Sale, More than 12 months, Estimated Fair Value	667
Available for Sale, Total Estimated Fair Value	272,825
Available for Sale, Less than 12 months, Unrealized Losses	2,529
Available for Sale, More than 12 Months, Unrealized Losses	27
Available for Sale, Total Unrealized Losses	2,556
Residential Mortgage-Backed Securities [Member]
Available for Sale, Less than 12 months, Estimated Fair Value	352
Available for Sale, More than 12 months, Estimated Fair Value
Available for Sale, Total Estimated Fair Value	352
Available for Sale, Less than 12 months, Unrealized Losses	2
Available for Sale, More than 12 Months, Unrealized Losses
Available for Sale, Total Unrealized Losses	2
States and Political Subdivisions [Member]
Held To Maturity, Less than 12 Months, Estimated Fair Value	23,446
Held To Maturity, More than 12 Months, Estimated Fair Value
Held To Maturity, Total Estimated Fair Value	23,446
Held To Maturity, Less than 12 Months, Unrealized Losses	345
Held To Maturity, More than 12 Months, Unrealized Losses
Held To Maturity, Total Unrealized Losses	345
Available for Sale, Less than 12 months, Estimated Fair Value	271,806
Available for Sale, More than 12 months, Estimated Fair Value	667
Available for Sale, Total Estimated Fair Value	272,473
Available for Sale, Less than 12 months, Unrealized Losses	2,527
Available for Sale, More than 12 Months, Unrealized Losses	27
Available for Sale, Total Unrealized Losses	$ 2,554

This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized neither as held-to-maturity nor trading securities.

Name:	cfr_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses1
Namespace Prefix:	cfr
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the excess of amortized cost basis over fair value of securities in a loss position and which are categorized neither as held-to-maturity nor trading securities.

+ Details

Name:	cfr_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses1
Namespace Prefix:	cfr
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the excess of amortized cost basis over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized neither as held-to-maturity nor trading securities.

+ Details

Name:	cfr_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses1
Namespace Prefix:	cfr
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities in an unrealized loss position which are categorized neither as held-to-maturity nor trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Emerging Issues Task Force (EITF)
-Number 03-1
-Paragraph 21
-Subparagraph a(2)

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name FASB Staff Position (FSP)
-Number FAS115-1/124-1
-Paragraph 17
-Subparagraph a(1)

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for less than twelve months.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the excess of [amortized] cost over fair value of securities that have been in a loss position for twelve months or longer for those securities which are categorized as held-to-maturity.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the excess of [amortized] cost over fair value of securities in a loss position and which are categorized as held-to-maturity.

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAggregateLosses
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities categorized as held-to-maturity which are in an unrealized loss position.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the excess of [amortized] cost over fair value of securities that have been in a loss position for less than twelve months for those securities which are categorized as held-to-maturity.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities categorized as held-to-maturity that have been in a continuous unrealized loss position for less than twelve months.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the fair value of securities categorized as held-to-maturity securities that have been in a continuous unrealized loss position for twelve months or longer.

+ References

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant