Pending Merger with Trustmark Corporation - Additional Information (Detail) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	May 29, 2012 Definitive merger agreement with Trustmark Corporation
Business Acquisition [Line Items]
Merger agreement, share exchange ratio for each share of BancTrust common stock			0.125
Merger agreement, preferred stock and associated warrants trustmark agreed to repurchase	50	50	50,000

Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29

-Article 5

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.28)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant