Condensed Parent Company Only Financial Statements - Condensed Statements of Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating income
Other income	$ 19,945	$ 15,896	$ 18,004
Operating expenses
Interest expense	320,362	208,381	104,937
Salaries and employee benefits expense	411,869	414,741	379,527
Other expenses	29,349	24,356	26,281
Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries	499,593	402,527	292,879
Income tax expense (benefit)	115,438	32,278	150,466
Net income	384,155	370,249	142,413
Less: Preferred stock dividends	(12,602)	(9,095)	(9,095)
Net income available to common shareholders	371,553	361,154	133,318
IBERIABANK Corporation
Operating income
Reimbursement of management expenses	85,796	83,262	76,177
Other income	190,407	245,213	146,796
Total operating income	276,203	328,475	222,973
Operating expenses
Interest expense	6,088	6,008	5,168
Salaries and employee benefits expense	62,938	55,436	55,013
Other expenses	25,106	28,963	32,965
Total operating expenses	94,132	90,407	93,146
Income (loss) before income tax benefit and increase in equity in undistributed earnings of subsidiaries	182,071	238,068	129,827
Income tax expense (benefit)	(600)	799	3,123
Income (loss) before equity in undistributed earnings of subsidiaries	182,671	237,269	126,704
Equity in undistributed earnings of subsidiaries	201,484	132,980	15,709
Net income	384,155	370,249	142,413
Less: Preferred stock dividends	12,602	9,095	9,095
Net income available to common shareholders	$ 371,553	$ 361,154	$ 133,318