Loans and Leases - Recorded Investment in Each Class of Total Loans and Leases by Credit Quality Indicator (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 23,381,000	$ 25,789,000
Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	22,405,000	24,915,000
Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	976,000	874,000
Investment grade
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	18,104,000	20,473,000
Investment grade | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	17,128,000	19,599,000
Investment grade | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	976,000	874,000
Speculative
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,277,000	5,308,000
Speculative | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	5,277,000	5,308,000
Speculative | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 0	0
Substandard
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		8,000
Substandard | Commercial and Financial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		8,000
Substandard | Commercial Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases		$ 0