Goodwill and Other Intangible Assets - Schedule of Carrying Amount of Goodwill (Detail) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2014
Goodwill [Roll Forward]
Beginning balance	$ 724,603
Goodwill adjustments during the period	4,985	$ 207,077
Ending balance	729,588	517,526
Operating Segments | IBERIABANK
Goodwill [Roll Forward]
Beginning balance	696,260
Goodwill adjustments during the period	4,985	207,077
Ending balance	701,245	489,183
Operating Segments | IMC
Goodwill [Roll Forward]
Beginning balance	23,178
Goodwill adjustments during the period	0	0
Ending balance	23,178	23,178
Operating Segments | LTC
Goodwill [Roll Forward]
Beginning balance	5,165
Goodwill adjustments during the period	0	0
Ending balance	$ 5,165	$ 5,165