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Securities - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2019 | Dec. 31, 2018 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018 | Dec. 31, 2007
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Gross gains |  |  | $ 0 |  | $ 0 | $ 3,600 |
Debt Securities, Available-for-sale, Realized Loss | $ 0 |  |  | $ 0 |  |  |
Gain (loss) on sale of equity securities | 0 |  | $ 0 | 295 | $ (14) |  |
Collateral Pledged [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Debt Securities, Available-for-sale, Restricted | $ 2,200 | $ 2,700 |  | $ 2,200 |  | 2,700 |
Other Investments [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Investments, Fair Value Disclosure |  | 3,427 |  |  |  | 3,427 |
Fair Value, Inputs, Level 3 [Member] | Other Investments [Member] | Fair Value, Measurements, Nonrecurring [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Investments, Fair Value Disclosure |  | $ 3,427 |  |  |  | $ 3,427 |
Common Class B [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Sale of Stock, Number of Shares Issued in Transaction |  | (25,702) |  |  |  |  |
Visa Inc's Initial Public Offering [Member] | Common Class B [Member] |  |  |  |  |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |  |  |  |  |
Sale of Stock, Number of Shares Issued in Transaction |  |  |  |  |  |  | (51,404)
Shares, Outstanding |  | (25,702) |  |  |  | (25,702) |

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