Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 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	$ 35,700		$ 35,700			$ 33,300
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	6,450,000		6,450,000			6,360,000
Advances from Federal Home Loan Banks						175,200
Federal Home Loan Bank Advances, Current Borrowing Capacity	6,260,000		6,260,000			6,180,000
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums	500		500			100
Loans and Leases Receivable, Gross, Carrying Amount, Covered	50,200		50,200
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	2,090,000		2,090,000			2,190,000
Reclassification of portfolio loans to loans held for sale			(23,948)	$ 0
Loans held for sale	52,837		52,837			45,505
Proceeds from sales of portfolio loans			24,247	0
Accretion	11,900	$ 14,200	29,648	32,188
Goodwill recorded for First South Bancorp	296,764		296,764			236,347
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	100,701		100,701			84,546
Remaining discount	93,000		93,000			95,500
Accretion Income	3,300	$ 4,100	6,500	$ 7,000
PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	4,300		4,300			1,300
Biscayne Bancshares
Financing Receivable, Recorded Investment [Line Items]
Assets					$ 1,029,184
Intangible assets					4,745
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities					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	183,700		183,700
Loans Pledged as Collateral	9,160,000		9,160,000			9,120,000
Federal Home Loan Bank of Chicago
Financing Receivable, Recorded Investment [Line Items]
Advances from Federal Home Loan Banks	13,500		13,500
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 2,730,000		$ 2,730,000			$ 2,940,000