Loans and Leases (Narrative) (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Jan. 01, 2020
Financing Receivable, Recorded Investment [Line Items]
Loans held for sale	$ 124,800	$ 67,900
Proceeds from Sale of Loans Receivable	1,050,000	756,000
Gain on sale of mortgage loans		300
Net deferred fees on non-PCI loans	50,200	900
Nonaccruing	191,483		$ 168,717
Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Purchase Discount Remaining	19,500	30,900
Loans and leases greater than 90 days and accruing	5,862
SBA-PPP
Financing Receivable, Recorded Investment [Line Items]
Net deferred fees on non-PCI loans	41,100
Loans Held For Sale
Financing Receivable, Recorded Investment [Line Items]
Proceeds from Sale of Loans Receivable		731,800
Portfolio Loans
Financing Receivable, Recorded Investment [Line Items]
Proceeds from Sale of Loans Receivable	7,600	24,200
Non-PCI Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing		114,946
Loans and leases greater than 90 days and accruing		3,291
Non-PCI Loans \| Commercial
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	43,322	42,407	42,407
Loans and leases greater than 90 days and accruing	4,312	1,094
PCD Loans
Financing Receivable, Recorded Investment [Line Items]
Nonaccruing	54,939		$ 53,771
Loans and leases greater than 90 days and accruing	355
Financing Receivable, Recorded Investment, Nonaccrual Status, Remaining Discount	45,300	88,200
Medical and Dental
Financing Receivable, Recorded Investment [Line Items]
Loans in the medical, dental or related field	$ 5,540,000	$ 5,160,000
Medical, dental or related fields percentage of total loans and leases	16.90%	17.90%
Federal Home Loan Bank of Atlanta
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	$ 12,157,153	$ 9,407,688
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	8,637,844	6,574,636
Advances from Federal Home Loan Banks	652,675	563,690
Federal Home Loan Bank Advances, Current Borrowing Capacity	7,985,169	6,010,946
Federal Reserve Bank
Financing Receivable, Recorded Investment [Line Items]
Loans Pledged as Collateral	4,104,866	3,684,919
Federal Reserve Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	3,321,762	2,981,712
Federal Reserve Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds	$ 3,321,762	$ 2,981,712

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Carrying amount of total receivables of a designated industry disclosed as a concentration risk.

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Federal Reserve Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds

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Amount of the collateral pledged in support of Federal Reserve Bank advances.

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Financing Receivable, Recorded Investment, Nonaccrual Status, Remaining Discount

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Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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Amount of advances or credit lines available from the Federal Home Loan Bank (FHLB).

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The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans made to finance real estate acquisitions. This element refers to the gain (loss) and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

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Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

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Amount, after valuation allowance, of financing receivable held for sale and not part of disposal group. Excludes loan covered under loss sharing agreement and loan classified as investment in debt security.

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The cash inflow associated with the sale of loans receivables arising from the financing of goods and services.

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Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

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