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Investment Securities Available for Sale - Narrative (Details) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2019 | Mar. 31, 2018 | Dec. 31, 2018
Schedule of Investments [Line Items] |  |  |
Proceeds from sales of investment securities | $ 56,800,000 | $ 10,100,000 |
Realized net (loss) gain on sales of investment securities available for sale | $ (16,800,000) | (3,400,000) |
Contractual maturities (up to) | 30 years |  |
Weighted average life of available for sale securities portfolio | 8 years 99 days |  | 5 years 270 days
Gross unrealized losses | $ 22,174,000 |  | $ 40,126,000
Other-than-temporary impairment recorded in earnings | 0 | $ 0 |
Agency RMBS |  |  |
Schedule of Investments [Line Items] |  |  |
Gross unrealized losses | 21,759,000 |  | 38,284,000
Non-Agency RMBS |  |  |
Schedule of Investments [Line Items] |  |  |
Gross unrealized losses | $ 415,000 |  | $ 1,466,000

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- Definition Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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