Acquired Loans - Changes in the Carrying Value of Acquired Loans (Details) - USD ($) $ in Thousands		6 Months Ended			12 Months Ended
		Jun. 30, 2018		Jun. 30, 2017	Dec. 31, 2017	Apr. 07, 2017
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		$ 257,438
Additions						$ 7,900
Accretion to interest income		5,927		$ 7,278
Carrying value, net, ending		170,061			$ 257,438
Acquired Not ASC 310-30 [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning	[1]	77,868		42,743	42,743
Transfers	[1],[2]	(29,212)			(36,719)
Additions	[1],[3]				109,548
Accretion to interest income	[1]	567			1,578
Payments received, net	[1]	(15,172)			(39,208)
Other	[1],[4]	96			(74)
Change in allowance for loan losses, acquired loans	[1]	0			0
Carrying value, net, ending	[1]	34,147			77,868
Acquired Impaired [Member]
Carrying value of acquired loans [Abstract]
Carrying value, net, beginning		179,570		$ 218,107	218,107
Transfers		(14,609)	[5]		0
Additions	[3]				7,899
Accretion to interest income		5,927			14,924
Payments received, net		(36,256)			(68,317)
Other	[4]	249			(361)
Change in allowance for loan losses, acquired loans		1,033			7,318
Carrying value, net, ending		$ 135,914			$ 179,570

[1] “Acquired Not ASC 310-30” loans consist of loans that are not in scope for FASB ASC Topic 310-30.

[2] “Acquired Not ASC 310-30” loans transferred to LHFI due to the discount on these loans being fully amortized.

[3] Loans acquired in the Reliance merger on April 7, 2017.

[4] Includes miscellaneous timing adjustments as well as acquired loan terminations through foreclosure, charge-off and other terminations.

[5] During the second quarter of 2018, Trustmark transferred the remaining loans acquired in the Bay Bank merger on March 16, 2012 from acquired impaired loans to LHFI.