Acquisitions and Divestitures - (Narrative) (Details) $ in Thousands				3 Months Ended
	Mar. 23, 2018 USD ($) branch	Nov. 30, 2017 USD ($) branch shares	Apr. 03, 2017 USD ($)	Mar. 31, 2018 USD ($) branch	Dec. 31, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Business Acquisition [Line Items]
Goodwill				$ 1,398,501	$ 1,386,853	$ 191,371	$ 191,371
Number of branches divested | branch				2
Deposits disposed of					$ 22,600
Capital Bank Financial Corp
Business Acquisition [Line Items]
Business acquisition, equity interest issued or issuable, number of shares (in shares) | shares		92,042,232
Payments to acquire businesses		$ 423,600		$ 423,592
Business combination, consideration transferred		$ 2,200,000		2,216,333
Number of bank branches | branch		178
Assets acquired				9,867,741
Loans				7,276,741
Securities available-for-sale				1,193,393
Deposits				8,140,102
Goodwill				1,158,549
Loans held-for-sale				125,344
Trading securities				0
Securities sold under agreements to repurchase				$ 26,664
Coastal Securities, Inc
Business Acquisition [Line Items]
Payments to acquire businesses			$ 131,000
Assets acquired			418,000
Goodwill			45,000
Loans held-for-sale			236,000
Trading securities			139,000
Securities sold under agreements to repurchase			202,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Fixed Income Payables			$ 96,000
Apex Bank
Business Acquisition [Line Items]
Number of branches divested | branch	2
Deposits disposed of	$ 30,000
Loans disposed of	$ 2,000