Condensed Parent Company Only Financial Statements - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flow from Operating Activities
Net income	$ 384,155	$ 370,249	$ 142,413
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16,360	(7,534)	(4,113)
Other operating activities, net	180,506	(204,998)	(30,991)
Cash Flow from Investing Activities
Purchases of premises and equipment, net of premises and equipment acquired	(35,000)	(13,730)	(37,763)
Other investing activities, net	1,000	343	636
Cash Flow from Financing Activities
Cash dividends paid on common stock	(92,190)	(84,782)	(72,772)
Cash dividends paid on preferred stock	(12,602)	(9,095)	(9,095)
Payments to repurchase common stock	(204,740)	(148,855)	0
Net proceeds from issuance of common stock	0	0	485,151
Net proceeds from issuance of preferred stock	96,388	0	0
Cash and Cash Equivalents at Beginning of Period	690,453
Cash and Cash Equivalents at End of Period	894,723	690,453
IBERIABANK Corporation
Cash Flow from Operating Activities
Net income	384,155	370,249	142,413
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	309	145	62
Net income of subsidiaries	(391,484)	(377,974)	(160,206)
Share-based compensation cost	24,584	20,278	16,436
Other operating activities, net	(9,828)	491	(4,256)
Net Cash Provided by Operating Activities	7,736	13,189	(5,551)
Cash Flow from Investing Activities
Cash paid in excess of cash received for acquisitions	0	(7)	(809,159)
Purchases of premises and equipment, net of premises and equipment acquired	(292)	(52)	(105)
Return of capital from (Capital contributed to) subsidiary	190,000	245,000	144,500
Other investing activities, net	(301)	(1,500)	0
Net Cash Used in Investing Activities	189,407	243,441	(664,764)
Cash Flow from Financing Activities
Cash dividends paid on common stock	(92,190)	(84,782)	(72,772)
Cash dividends paid on preferred stock	(12,602)	(9,095)	(9,095)
Net share-based compensation stock transactions	(3,373)	(3,226)	(832)
Payments to repurchase common stock	(204,740)	(148,855)	0
Net proceeds from issuance of common stock	0	0	485,151
Net proceeds from issuance of preferred stock	96,388	0	0
Other financing activities, net	0	0	(56)
Net Cash Provided by Financing Activities	(216,517)	(245,958)	402,396
Net Increase (Decrease) In Cash and Cash Equivalents	(19,374)	10,672	(267,919)
Cash and Cash Equivalents at Beginning of Period	179,545	168,873	436,792
Cash and Cash Equivalents at End of Period	$ 160,171	$ 179,545	$ 168,873