Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Acquisition [Line Items]
Merger and integration expense	$ 4,865	$ 8,647	$ 9,037	$ 14,307
Professional fees
Business Acquisition [Line Items]
Merger and integration expense	1,327	4,478	2,126	6,345
Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	87	1,472	483	2,989
Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	420	17	726	17
Occupancy
Business Acquisition [Line Items]
Merger and integration expense	(82)	1,505	(107)	1,623
Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	503	79	1,325	1,148
All other expense
Business Acquisition [Line Items]
Merger and integration expense	2,610	$ 1,096	4,484	$ 2,185
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Merger and integration expense	9,456		11,061
IBERIABANK (IBKC) | Professional fees
Business Acquisition [Line Items]
Merger and integration expense	3,748		4,410
IBERIABANK (IBKC) | Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	4,705		5,394
IBERIABANK (IBKC) | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	$ 1,003		$ 1,257