Acquisitions and Divestitures - Merger and Integration Expenses (Details) - Capital Bank Financial Corporation - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Merger and integration expense	$ 10,190	$ 6,991	$ 82,052	$ 11,622
Professional fees
Business Acquisition [Line Items]
Merger and integration expense	4,594	3,492	19,215	8,004
Employee compensation, incentives and benefits
Business Acquisition [Line Items]
Merger and integration expense	1,965	232	8,459	232
Contract employment and outsourcing
Business Acquisition [Line Items]
Merger and integration expense	599	351	3,702	351
Occupancy
Business Acquisition [Line Items]
Merger and integration expense	100	15	2,321	15
Miscellaneous expense
Business Acquisition [Line Items]
Merger and integration expense	1,384	130	6,522	234
All other expense
Business Acquisition [Line Items]
Merger and integration expense	$ 1,548	$ 2,771	$ 41,833	$ 2,786