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Investment Securities Available for Sale - Narrative (Details) - USD ($) | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | ---
Sep. 30, 2019 | Sep. 30, 2018 | Sep. 30, 2019 | Sep. 30, 2018 | Dec. 31, 2018
Schedule of Investments [Line Items] |  |  |  |  |
Proceeds from sales of investment securities | $ 41,200,000 |  | $ 98,000,000.0 | $ 26,900,000 |
Realized net gain (loss) on sales of investment securities available for sale | 5,000,000.0 |  | $ 21,800,000 | (12,300,000) |
Contractual maturities (up to) |  |  | 41 years |  |
Weighted average life of available for sale securities portfolio |  |  | 5 years 7 months 6 days |  | 5 years 8 months 12 days
Gross unrealized losses | (8,323,000) |  | $ (8,323,000) |  | $ (40,126,000)
Other-than-temporary impairment recorded in earnings | 0 | $ 0 | 0 | $ 0 |
Agency RMBS |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Gross unrealized losses | (7,977,000) |  | (7,977,000) |  | (38,284,000)
Non-Agency RMBS |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Gross unrealized losses | (192,000) |  | (192,000) |  | (1,466,000)
CMBS |  |  |  |  |
Schedule of Investments [Line Items] |  |  |  |  |
Gross unrealized losses | $ (154,000) |  | $ (154,000) |  | $ (376,000)

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- Definition Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 50 -Paragraph 4 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455 + Details
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