Business Segments - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Segment Reporting Information
Interest and dividend income	$ 171,077	$ 133,793	$ 470,207	$ 367,539
Interest expense	15,960	12,042	43,609	32,107
Net interest income	155,117	121,751	426,598	335,432
Provision for loan losses	5,062	5,714	19,197	12,565
Mortgage income	20,730	14,263	63,999	38,150
Title revenue	6,627	5,577	17,402	15,007
Other non-interest income	30,121	27,272	86,489	73,397
Allocated expenses	0	0	0	0
Non-interest expense	144,968	120,112	431,330	354,479
Income before income tax expense	62,565	43,037	143,961	94,942
Income tax expense	20,090	12,144	45,524	25,497
Net Income	42,475	30,893	98,437	69,445
Total loans and loans held for sale	14,319,187	11,229,417	14,319,187	11,229,417
Total assets	19,534,225	15,514,449	19,534,225	15,514,449	$ 15,757,904
Total deposits	16,303,065	12,377,691	16,303,065	12,377,691	$ 12,520,525
Average assets	19,604,070	15,476,208	18,015,680	14,300,952
Operating Segments | IBERIABANK
Segment Reporting Information
Interest and dividend income	169,005	131,987	464,775	362,974
Interest expense	15,109	11,416	41,410	30,784
Net interest income	153,896	120,571	423,365	332,190
Provision for loan losses	5,062	5,621	19,197	12,481
Mortgage income	365	(4)	932	80
Title revenue	0	0	0	0
Other non-interest income	30,120	27,310	86,498	73,459
Allocated expenses	(3,518)	(2,386)	(11,603)	(9,110)
Non-interest expense	124,909	104,172	373,948	308,515
Income before income tax expense	57,928	40,470	129,253	93,843
Income tax expense	18,253	11,128	39,695	25,038
Net Income	39,675	29,342	89,558	68,805
Total loans and loans held for sale	14,094,936	11,057,497	14,094,936	11,057,497
Total assets	19,242,690	15,288,142	19,242,690	15,288,142
Total deposits	16,293,681	12,371,522	16,293,681	12,371,522
Average assets	19,321,164	15,240,567	17,760,033	14,097,954
Operating Segments | IMC
Segment Reporting Information
Interest and dividend income	2,071	1,805	5,430	4,563
Interest expense	851	626	2,199	1,323
Net interest income	1,220	1,179	3,231	3,240
Provision for loan losses	0	93	0	84
Mortgage income	20,365	14,267	63,067	38,070
Title revenue	0	0	0	0
Other non-interest income	1	(36)	(2)	(60)
Allocated expenses	2,693	1,697	8,685	6,432
Non-interest expense	15,605	11,624	44,259	33,558
Income before income tax expense	3,288	1,996	13,352	1,176
Income tax expense	1,306	785	5,286	473
Net Income	1,982	1,211	8,066	703
Total loans and loans held for sale	224,251	171,920	224,251	171,920
Total assets	264,914	200,778	264,914	200,778
Total deposits	9,384	6,169	9,384	6,169
Average assets	256,897	210,345	230,379	177,995
Operating Segments | LTC
Segment Reporting Information
Interest and dividend income	1	1	2	2
Interest expense	0	0	0	0
Net interest income	1	1	2	2
Provision for loan losses	0	0	0	0
Mortgage income	0	0	0	0
Title revenue	6,627	5,577	17,402	15,007
Other non-interest income	0	(2)	(7)	(2)
Allocated expenses	825	689	2,918	2,678
Non-interest expense	4,454	4,316	13,123	12,406
Income before income tax expense	1,349	571	1,356	(77)
Income tax expense	531	231	543	(14)
Net Income	818	340	813	(63)
Total loans and loans held for sale	0	0	0	0
Total assets	26,621	25,529	26,621	25,529
Total deposits	0	0	0	0
Average assets	$ 26,009	$ 25,296	$ 25,268	$ 25,003