Defined Benefit and Other Postretirement Benefits (Details) (USD $)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2014
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	$ 123,000	$ 148,000	$ 372,000	$ 446,000
Interest cost	1,328,000	1,252,000	3,971,000	3,506,000
Expected return on plan assets	(1,563,000)	(2,060,000)	(4,681,000)	(5,660,000)
Recognized net loss due to settlement	1,709,000	838,000	2,459,000	1,363,000
Recognized net actuarial (gain) loss	(1,701,000)	1,374,000	(229,000)	4,142,000
Net periodic benefit cost	(104,000)	1,552,000	1,892,000	3,797,000
Expected minimum required contribution, prior to HAFTA					1,800,000
Expected minimum required contribution, after HAFTA					0
Actual contribution			1,000,000
Supplemental Retirement Plan [Member]
Net periodic benefit cost [Abstract]
Service cost	74,000	150,000	222,000	448,000
Interest cost	548,000	484,000	1,650,000	1,452,000
Amortization of prior service cost	63,000	62,000	188,000	188,000
Recognized net actuarial (gain) loss	164,000	260,000	497,000	778,000
Net periodic benefit cost	$ 849,000	$ 956,000	$ 2,557,000	$ 2,866,000