Defined Benefit and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Trustmark Capital Accumulation Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	$ 140,000	$ 137,000
Interest cost	945,000	1,115,000
Expected return on plan assets	(1,400,000)	(1,471,000)
Recognized net actuarial loss	1,309,000	1,037,000
Net periodic benefit cost	994,000	818,000
Years of service required to vest (in years)		3 Y
Contribution			1,000,000
Minimum required contribution	3,000,000
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	170,000	147,000
Interest cost	517,000	569,000
Amortization of prior service cost	62,000	59,000
Recognized net actuarial loss	215,000	124,000
Net periodic benefit cost	$ 964,000	$ 899,000