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Investment Securities - Narrative (Details) |  | 3 Months Ended | 6 Months Ended |
--- | --- | --- | --- | ---
Jan. 01, 2019 USD ($) | Jun. 30, 2019 USD ($) Investments | Jun. 30, 2018 USD ($) | Jun. 30, 2019 USD ($) Investments | Jun. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Investment securities classified as held to maturity |  | $ 98,800,000 |  | $ 98,800,000 |  | $ 406,800,000
Amortized cost of held to maturity securities transferred | $ 281,100,000 |  |  |  |  |
Fair value of held to maturity securities | $ 275,000,000.0 |  |  |  |  |
Unrealized loss |  |  |  | $ 6,000,000.0 |  |
Investment securities in an unrealized loss position (securities) | Investments |  | 397 |  | 397 |  | 760
Impairment loss |  | $ 0 | $ 0 | $ 0 | $ 0 |
Callable Within One Year |  |  |  |  |  |
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |  |  |
Amortized cost of investment securities callable after one year but within five years |  | 153,600,000 |  | 153,600,000 |  |
Fair value of investment securities callable after one year but within five years |  | 153,900,000 |  | 153,900,000 |  |
Callable structured notes amortized costs |  | 2,000,000.0 |  | 2,000,000.0 |  |
Callable structured notes fair value |  | $ 2,000,000 |  | $ 2,000,000 |  |

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- Definition Amount of investment in debt security, measured at amortized cost, transferred to investment in debt security, measured at fair value, with change in fair value recognized in other comprehensive income (available-for-sale) and net income (trading). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27405-111563 + Details
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