Acquisitions and Divestitures - Merger and Integration Expenses (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
IBERIABANK Corporation
Business Acquisition [Line Items]
Merger and integration expense	$ 11,371
IBERIABANK Corporation | Professional fees
Business Acquisition [Line Items]
Merger and integration expense	8,228
IBERIABANK Corporation | Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	3,079
IBERIABANK Corporation | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	64
Capital Bank Financial Corporation
Business Acquisition [Line Items]
Merger and integration expense	22,870	$ 92,393	$ 56,748
Capital Bank Financial Corporation | Professional fees
Business Acquisition [Line Items]
Merger and integration expense	11,221	22,337	28,151
Capital Bank Financial Corporation | Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	1,189	9,613	17,077
Capital Bank Financial Corporation | Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	240	3,681	1,270
Capital Bank Financial Corporation | Occupancy
Business Acquisition [Line Items]
Merger and integration expense	1,453	5,236	15
Capital Bank Financial Corporation | Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	2,072	7,652	1,291
Capital Bank Financial Corporation | All other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 6,695	$ 43,874	$ 8,944