Defined Benefit and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Trustmark Capital Accumulation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Years of service required to vest			3 years
Net periodic benefit cost [Abstract]
Service cost	$ 148,000	$ 134,000	$ 446,000	$ 413,000
Interest cost	1,252,000	947,000	3,506,000	2,837,000
Expected return on plan assets	(2,060,000)	(1,438,000)	(5,660,000)	(4,238,000)
Recognized net loss due to Settlement	838,000	0	1,363,000	0
Recognized net actuarial loss	1,374,000	1,303,000	4,142,000	3,922,000
Net periodic benefit cost	1,552,000	946,000	3,797,000	2,934,000
Period of average interest rate before MAP-21			2 years
Period of average interest rate after MAP-21			25 years	25 years
Pension funding contributions cap percentage (in hundredths)			115.00%		110.00%
Pension funding contributions floor percentage (in hundredths)			85.00%		90.00%
Minimum required contribution			2,100,000		1,500,000
Change in minimum required contribution			600,000
Defined Benefit Plan, Effective Interest Rate			6.13%		6.82%
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	150,000	170,000	448,000	510,000
Interest cost	484,000	517,000	1,452,000	1,550,000
Amortization of prior service credits	62,000	63,000	188,000	188,000
Recognized net actuarial loss	260,000	215,000	778,000	645,000
Net periodic benefit cost	$ 956,000	$ 965,000	$ 2,866,000	$ 2,893,000