Securities (Net Gains and Losses on Trading Account Securities) (Details) (USD $) In Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Securities
Net gain on sales transactions	$ 161	$ 398	$ 469	$ 880
Net mark-to-market gains	7	71	7	123
Net gain on trading account securities	$ 168	$ 469	$ 476	$ 1,003

Securities

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Namespace Prefix:	cfr
Data Type:	xbrli:stringItemType
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- Definition

This item represents the difference between the gross amount of gains and losses included in earnings for transfers of securities from the available-for-sale category into the trading category. Such net gain or loss included in earnings represents the net unrealized gain or loss which had been included in other comprehensive income and is associated with the securities transferred from the available-for-sale category to the trading category.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 115
-Paragraph 21
-Subparagraph d

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesTransfersToTradingGainsLossesNet
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

This item represents the gain realized during the period from the sale of trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph c
-Article 5

+ Details

Name:	us-gaap_TradingSecuritiesRealizedGain
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Data Type:	xbrli:monetaryItemType
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- Definition

This item represents the gain or loss realized during the period from the sale of trading securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 7
-Subparagraph c
-Article 5

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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