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Investment Securities - Narrative (Details) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Jun. 30, 2020 USD ($) Investments | Sep. 30, 2018 USD ($) | Sep. 30, 2018 USD ($) | Dec. 31, 2019 USD ($) Investments
Schedule of Held-to-maturity Securities [Line Items] |  |  |  |
Investment securities classified as held to maturity | $ 67,900,000 |  |  | $ 92,300,000
Investment securities in an unrealized loss position (securities) | Investments | 142 |  |  | 331
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 | 245,000,000.0 |  |  |
Fair value of investment securities callable after one year but within five years | 245,700,000 |  |  |
Callable structured notes amortized costs | $ 0 |  |  |

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- Definition Available-for-Sale and Held-to-Maturity, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions + References No definition available. + Details
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- Definition Investment Securities,Callable Structured, Amortized Cost Basis + References No definition available. + Details
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- Definition Investment Securities, Primarily Classified as Available-for-Sale, Debt Maturities, Rolling Year Two Through Five, Amortized Cost Basis + References No definition available. + Details
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- Definition Investment Securities, Primarily Classified as Available-for-Sale, Debt Maturities, Rolling Year Two Through Five, Fair Value + References No definition available. + Details
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- Definition Amount of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121553693&loc=d3e26610-111562 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03(6)) -URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878 + Details
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- Definition The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 8A -URI http://asc.fasb.org/extlink&oid=121553693&loc=SL6284422-111562 + Details
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