Loans and Leases - Recorded Investment in Each Class of Total Loans and Leases by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 23,372,000	$ 23,294,000
Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	22,520,000	22,533,000
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	602,000	98,000
Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	250,000	663,000
Investment grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	18,605,000	18,627,000
Investment grade | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	17,753,000	17,866,000
Investment grade | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	602,000	98,000
Investment grade | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	250,000	663,000
Speculative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	4,728,000	4,638,000
Speculative | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	4,728,000	4,638,000
Speculative | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Speculative | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Special Mention
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	39,000	29,000
Special Mention | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	39,000	29,000
Special Mention | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0	0
Special Mention | Lease Financing
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 0	$ 0