Shareholders' Equity, Capital Ratios and Other Regulatory Matters - Shareholders' Equity, Capital Ratios and Other Regulatory Matters (Details) - USD ($) $ / shares in Units, $ in Thousands						3 Months Ended	12 Months Ended
	Aug. 01, 2024	May 01, 2024	Apr. 04, 2019	May 09, 2016	Aug. 05, 2015	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)							23,750	13,750
Preferred stock, par value (in usd per share)							$ 1	$ 1
Liquidation preference (in usd per share)							$ 10,000	$ 10,000
Liquidation Amount				$ 237,500
Shares authorized to be repurchased (in shares)							1,165,000
Series B Preferred Stock
Class of Stock [Line Items]
Annual Dividend Rate					6.625%
Liquidation Amount					$ 80,000
Series B Preferred Stock | 3 Month LIBOR Rate
Class of Stock [Line Items]
Variable dividend rate per share					4.262%
Series C Preferred Stock
Class of Stock [Line Items]
Annual Dividend Rate				6.60%
Liquidation Amount				$ 57,500
Series C Preferred Stock | 3 Month LIBOR Rate
Class of Stock [Line Items]
Variable dividend rate per share				4.92%
Series D Preferred Stock
Class of Stock [Line Items]
Preferred Stock, Ownership Interest Per Depositary Share			0.25%
Annual Dividend Rate			6.10%
Preferred stock, par value (in usd per share)			$ 1.00
Liquidation preference (in usd per share)			$ 10,000
Liquidation Amount			$ 100,000
Series D Depositary Shares
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)			4,000,000
Liquidation preference (in usd per share)			$ 25
Common Stock
Class of Stock [Line Items]
Common stock repurchases (in shares)							(2,700,000)	(1,972,500)
2018 Share Repurchase Plan | Common Stock
Class of Stock [Line Items]
Number of shares authorized to be repurchased (in shares)								2,765,000
2019 Share Repurchase Program | Common Stock
Class of Stock [Line Items]
Number of shares authorized to be repurchased (in shares)						1,600,000
Stock repurchase percentage						3.00%
2016 and 2018 Share Repurchase Program
Class of Stock [Line Items]
Average cost of common stock shares repurchased (in usd per share)							$ 75.83	$ 75.46
2016 and 2018 Share Repurchase Program | Common Stock
Class of Stock [Line Items]
Common stock repurchases (in shares)							2,700,000	1,972,500
Common stock repurchased, weighted average price							$ 204,700	$ 148,900
IBERIABANK
Class of Stock [Line Items]
Additional amount of dividends after annual earnings							199,600
Funds available for loans or advances by parent							$ 311,300
Forecast | Series D Preferred Stock
Class of Stock [Line Items]
Annual Dividend Rate		6.10%
Variable dividend rate per share	3.859%