Business Segments - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Segment Reporting Information
Interest and dividend income	$ 180,504	$ 171,077	$ 536,134	$ 470,207
Interest expense	17,087	15,960	48,561	43,609
Net interest income	163,417	155,117	487,573	426,598
Provision for loan losses	12,484	5,062	39,255	19,197
Mortgage income	21,807	20,628	67,738	63,897
Service charges on deposit accounts	11,066	11,342	32,957	30,766
Title revenue	6,001	6,627	16,881	17,402
Other non-interest income	20,947	18,881	63,007	55,825
Allocated expenses	0	0	0	0
Non-interest expense	138,139	144,968	415,095	431,330
Income before income tax expense	72,615	62,565	213,806	143,961
Income tax expense	24,547	20,090	72,159	45,524
Net Income	48,068	42,475	141,647	98,437
Total loans and loans held for sale, net of unearned income	15,135,365	14,319,187	15,135,365	14,319,187
Total assets	20,788,566	19,534,225	20,788,566	19,534,225	$ 19,504,068
Total deposits	16,522,517	16,303,065	16,522,517	16,303,065	$ 16,178,748
Average assets	20,392,828	19,604,070	20,020,715	18,015,680
IBERIABANK
Segment Reporting Information
Interest and dividend income	178,521	169,005	530,409	464,775
Interest expense	15,944	15,109	45,380	41,410
Net interest income	162,577	153,896	485,029	423,365
Provision for loan losses	12,443	5,062	39,214	19,197
Mortgage income	850	263	856	830
Service charges on deposit accounts	11,066	11,342	32,957	30,766
Title revenue	0	0	0	0
Other non-interest income	20,946	18,880	62,999	55,834
Allocated expenses	(3,914)	(3,518)	(10,468)	(11,603)
Non-interest expense	127,690	124,909	367,985	373,948
Income before income tax expense	59,220	57,928	185,110	129,253
Income tax expense	19,282	18,253	60,841	39,695
Net Income	39,938	39,675	124,269	89,558
Total loans and loans held for sale, net of unearned income	14,957,337	14,094,936	14,957,337	14,094,936
Total assets	20,537,304	19,242,690	20,537,304	19,242,690
Total deposits	16,513,867	16,293,681	16,513,867	16,293,681
Average assets	20,061,071	19,321,164	19,705,052	17,760,033
IMC
Segment Reporting Information
Interest and dividend income	1,982	2,071	5,723	5,430
Interest expense	1,143	851	3,181	2,199
Net interest income	839	1,220	2,542	3,231
Provision for loan losses	41	0	41	0
Mortgage income	20,957	20,365	66,882	63,067
Service charges on deposit accounts	0	0	0	0
Title revenue	0	0	0	0
Other non-interest income	1	1	8	(2)
Allocated expenses	3,010	2,693	8,007	8,685
Non-interest expense	5,891	15,605	33,909	44,259
Income before income tax expense	12,855	3,288	27,475	13,352
Income tax expense	5,048	1,306	10,826	5,286
Net Income	7,807	1,982	16,649	8,066
Total loans and loans held for sale, net of unearned income	178,028	224,251	178,028	224,251
Total assets	226,906	264,914	226,906	264,914
Total deposits	8,650	9,384	8,650	9,384
Average assets	305,996	256,897	289,037	230,379
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
Service charges on deposit accounts	0	0	0	0
Title revenue	6,001	6,627	16,881	17,402
Other non-interest income	0	0	0	(7)
Allocated expenses	904	825	2,461	2,918
Non-interest expense	4,558	4,454	13,201	13,123
Income before income tax expense	540	1,349	1,221	1,356
Income tax expense	217	531	492	543
Net Income	323	818	729	813
Total loans and loans held for sale, net of unearned income	0	0	0	0
Total assets	24,356	26,621	24,356	26,621
Total deposits	0	0	0	0
Average assets	$ 25,761	$ 26,009	$ 26,626	$ 25,268