Defined Benefit and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Trustmark Capital Accumulation Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 124,000	$ 138,000	$ 398,000	$ 412,000
Interest cost	1,115,000	1,194,000	3,345,000	3,583,000
Expected return on plan assets	(1,470,000)	(1,481,000)	(4,412,000)	(4,444,000)
Recognized net actuarial loss	1,026,000	849,000	3,100,000	2,548,000
Net periodic benefit cost	795,000	700,000	2,431,000	2,099,000
Years of service required to vest (in years)			3 Y
Voluntary contribution					1,900,000
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	147,000	190,000	441,000	567,000
Interest cost	569,000	561,000	1,707,000	1,682,000
Amortization of prior service cost	59,000	38,000	177,000	114,000
Recognized net actuarial loss	124,000	88,000	372,000	266,000
Net periodic benefit cost	$ 899,000	$ 877,000	$ 2,697,000	$ 2,629,000