Loans and Leases - Recorded Investment in Each Class of Total Loans and Leases by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 27,009,000	$ 25,789,000
Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25,663,000	24,915,000
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1,346,000	874,000
Investment grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	21,953,000	20,473,000
Investment grade | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	20,607,000	19,599,000
Investment grade | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	1,346,000	874,000
Speculative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,017,000	5,308,000
Speculative | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,017,000	5,308,000
Speculative | Commercial Real Estate
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	25,000
Special mention | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	25,000
Special mention | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	0
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	14,000	8,000
Substandard | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	14,000	8,000
Substandard | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 0	$ 0