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Investment Securities - Non-Marketable Securities (Details) | 3 Months Ended |  |
--- | --- | --- | ---
Mar. 31, 2018 USD ($) $ / shares shares | Apr. 26, 2018 | Dec. 31, 2017 USD ($)
Schedule of Cost-method Investments [Line Items] |  |  |
Federal Home Loan Bank stock, par value (usd per share) | $ / shares | $ 100 |  |
Investments in low income housing tax credit funds | $ 5,000,000 |  | $ 2,100,000
Low income housing tax credits and other tax benefits | 110,000 |  |
Low income housing amortization expense | 94,000 |  |
Unfunded commitments for low income housing tax credit funds | $ 3,200,000 |  |
Visa Inc. | Visa Inc. Class B common stock |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Conversion rate on common stock | 1.6483 |  |
Visa Inc. Class B common stock |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Number of shares of securities carried at cost | shares | 16,939 |  |
Carrying value of securities carried at cost | $ 0 |  |
Fair value of Class B common stock | 3,300,000 |  | 3,200,000
Subsequent event |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Federal Home Loan Bank, dividend rate percentage |  | 7.00% |
Other assets |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |
Federal Home Loan Bank stock | $ 11,100,000 |  | $ 11,100,000

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