Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Apr. 02, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	$ 32,200		$ 32,200			$ 33,300
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	6,540,000		6,540,000			6,360,000
Advances from Federal Home Loan Banks						175,200
Federal Home Loan Bank Advances, Current Borrowing Capacity	6,350,000		6,350,000			6,180,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	200		200			100
Loans and Leases Receivable, Gross, Carrying Amount, Covered	47,300		47,300
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	2,780,000		2,780,000			2,190,000
Reclassification of portfolio loans to (from) loans held for sale			(23,900)
Loans held for sale	83,256		83,256			45,505
Proceeds from sales of portfolio loans			24,247	$ 0
Accretion	16,200	$ 13,500	45,891	45,699
Goodwill recorded for First South Bancorp	296,764		296,764			236,347
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	108,816		108,816			84,546
Remaining discount	85,000		85,000			95,500
Accretion Income	3,500	$ 2,900	10,000	$ 9,900
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	800		800			1,300
Biscayne Bancshares
Financing Receivable, Recorded Investment [Line Items]
Assets					$ 1,029,184
Intangible assets					4,745
Liabilities assumed					956,756
Deposits					786,512
Goodwill recorded for First South Bancorp					$ 46,521
Biscayne Bancshares | Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans acquired	850,352		850,352
Biscayne Bancshares | PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Loans acquired	13,032		13,032
Federal Home Loan Bank of Atlanta
Financing Receivable, Recorded Investment [Line Items]
Advances from Federal Home Loan Banks	181,700		181,700
Loans Pledged as Collateral	9,330,000		9,330,000			9,120,000
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 3,470,000		$ 3,470,000			$ 2,940,000