Business Segments - Schedule of Segment Reporting Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Segment Reporting Information
Interest and dividend income	$ 176,936	$ 138,585
Interest expense	15,533	12,781
Net interest income	161,403	125,804
Provision for loan losses	14,905	5,345
Mortgage income	20,347	18,023
Service charges on deposit accounts	10,951	9,262
Title revenue	4,745	4,629
Other non-interest income	19,802	16,985
Allocated expenses	0	0
Non-interest expense	137,452	133,153
Income before income tax expense	64,891	36,205
Income tax expense	22,122	11,079
Net Income	42,769	25,126
Total loans and loans held for sale, net of unearned income	14,643,789	13,088,505
Total assets	20,092,563	18,051,762	$ 19,504,068
Total deposits	16,260,566	14,665,024	$ 16,178,748
Average assets	19,661,311	15,957,613
Operating Segments | IBERIABANK
Segment Reporting Information
Interest and dividend income	175,324	136,830
Interest expense	14,654	12,290
Net interest income	160,670	124,540
Provision for loan losses	14,905	5,345
Mortgage income	406	(1)
Service charges on deposit accounts	10,951	9,262
Title revenue	0	0
Other non-interest income	19,803	16,989
Allocated expenses	(2,669)	(4,847)
Non-interest expense	120,027	116,005
Income before income tax expense	59,567	34,287
Income tax expense	20,001	10,313
Net Income	39,566	23,974
Total loans and loans held for sale, net of unearned income	14,428,613	12,869,096
Total assets	19,774,092	17,772,632
Total deposits	16,256,147	14,660,135
Average assets	19,381,718	15,750,918
Operating Segments | IMC
Segment Reporting Information
Interest and dividend income	1,611	1,754
Interest expense	879	491
Net interest income	732	1,263
Provision for loan losses	0	0
Mortgage income	19,941	18,024
Service charges on deposit accounts	0	0
Title revenue	0	0
Other non-interest income	(1)	(2)
Allocated expenses	2,050	3,528
Non-interest expense	13,198	12,916
Income before income tax expense	5,424	2,841
Income tax expense	2,153	1,122
Net Income	3,271	1,719
Total loans and loans held for sale, net of unearned income	215,176	219,409
Total assets	291,893	254,401
Total deposits	4,419	4,889
Average assets	252,281	181,942
Operating Segments | LTC
Segment Reporting Information
Interest and dividend income	1	1
Interest expense	0	0
Net interest income	1	1
Provision for loan losses	0	0
Mortgage income	0	0
Service charges on deposit accounts	0	0
Title revenue	4,745	4,629
Other non-interest income	0	(2)
Allocated expenses	619	1,319
Non-interest expense	4,227	4,232
Income before income tax expense	(100)	(923)
Income tax expense	(32)	(356)
Net Income	(68)	(567)
Total loans and loans held for sale, net of unearned income	0	0
Total assets	26,578	24,729
Total deposits	0	0
Average assets	$ 27,312	$ 24,753