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Securities - Narrative (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2018 | Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items] |  |  |
Realized gain |  | $ 3,572 | $ 0
Common Class B [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Number of shares sold | 25,702 |  |
Common Class B [Member] | Visa Inc's Initial Public Offering [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Number of shares sold |  | 51,404 |
Number of shares remaining | 25,702 | 25,702 |
Other investments | Fair Value, Measurements, Nonrecurring [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Other investments | $ 3,427 | $ 3,427 |
Fair Value, Inputs, Level 3 [Member] | Other investments | Fair Value, Measurements, Nonrecurring [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Other investments | $ 3,400 | $ 3,400 |

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