Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Business Acquisition [Line Items]
Merger and integration expense	$ 4,172	$ 5,660
Professional fees
Business Acquisition [Line Items]
Merger and integration expense	799	1,867
Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	396	1,517
Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	306	0
Occupancy
Business Acquisition [Line Items]
Merger and integration expense	(25)	118
Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	822	1,069
All other expense
Business Acquisition [Line Items]
Merger and integration expense	1,874	$ 1,089
IBERIABANK (IBKC)
Business Acquisition [Line Items]
Merger and integration expense	1,605
IBERIABANK (IBKC) | Professional fees
Business Acquisition [Line Items]
Merger and integration expense	662
IBERIABANK (IBKC) | Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	689
IBERIABANK (IBKC) | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	$ 254