Business Combinations (Details) (USD $) Share data in Thousands, unless otherwise specified	3 Months Ended			3 Months Ended	12 Months Ended		3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011	Mar. 31, 2012 Trustmark National Bank [Member] Heritage Banking Group Business Acquisition [Member]	Dec. 31, 2011 Trustmark National Bank [Member] Heritage Banking Group Business Acquisition [Member]	Apr. 15, 2011 Trustmark National Bank [Member] Heritage Banking Group Business Acquisition [Member]	Mar. 31, 2012 Trustmark National Bank [Member] Bay Bank & Trust Company [Member]	Mar. 16, 2012 Trustmark National Bank [Member] Bay Bank & Trust Company [Member]
Business Acquisition [Line Items]
Age of acquired entity (in years)						90		76
FDIC loss-share transaction asset coverage agreement						$ 151,900,000
FDIC loss-share agreement covered loan and other real estate losses (in hundredths)						80.00%
FDIC loss-share agreement term for single family residential mortgage loans and foreclosed real estate (in years)						10
FDIC loss-share agreement term for commercial loans and related foreclosures (in years)						5
FDIC loss-share agreement reimbursement term for recoveries of covered losses (in years)						3
Assets [Abstract]
Cash and due from banks						50,447,000		88,154,000
Federal funds sold						1,000,000		0
Securities available for sale						6,389,000		26,369,000
LHFI, excluding covered loans						9,644,000		98,053,000
Covered loans						97,770,000		0
Premises and equipment, net						55,000		9,466,000
Identifiable intangible assets						902,000		5,454,000
Other real estate								2,569,000
Other real estate at acquisition	5,824,000		6,331,000			7,485,000
FDIC indemnification asset						33,333,000		0
Other assets						218,000		4,014,000
Total Assets Acquired	234,079,000	0				207,243,000		234,079,000
Liabilities [Abstract]
Deposits						204,349,000		208,796,000
Short-term borrowings						23,157,000		0
Other liabilities						730,000		526,000
Total Liabilities						228,236,000		209,322,000
Net assets acquired at fair value						(20,993,000)		24,757,000
Consideration paid to Bay Bank				0				22,003,000
Cash received on acquisition					28,449,000		0
Bargain purchase gain	2,754,000	0			7,456,000		2,754,000
Income taxes					2,852,000		0
Bargain purchase gain, net of taxes					4,604,000		2,754,000
Added revenue in period from acquisition				3,100,000
Added net income available to common shareholders in the period from acquisition				1,700,000
Business acquisition, cost of acquired entity, cash paid								10,000,000
Business acquisition, equity issued (in shares)							510
Business acquisition, equity issued, value assigned								12,000,000
Finite-lived intangible assets, useful life (in years)							10
Business acquisition, total transaction expenses							2,600,000
Business acquisition, severance expense							672,000
Business acquisition, contract termination and other expenses							$ 1,900,000