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Investments - Gross Unrealized Losses and Fair Value for Mortgage-Backed in Unrealized Loss Position (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Less than 12 months |  |
Gross Unrealized Losses | $ (6,761) | $ (485)
Estimated Fair Value | 737,720 | 76,452
12 months or more |  |
Gross Unrealized Losses | (125) | 0
Estimated Fair Value | 5,869 | 0
Total |  |
Gross Unrealized Losses | (6,886) | (485)
Estimated Fair Value | 743,589 | 76,452
Mortgage-backed securities |  |
Less than 12 months |  |
Gross Unrealized Losses | (5,283) | (134)
Estimated Fair Value | 277,142 | 46,011
12 months or more |  |
Gross Unrealized Losses | (125) | 0
Estimated Fair Value | 5,869 | 0
Total |  |
Gross Unrealized Losses | (5,408) | (134)
Estimated Fair Value | 283,011 | 46,011
Utah Housing Corporation bonds |  |
Less than 12 months |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
12 months or more |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
Total |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
U.S. government-sponsored enterprises and Treasuries |  |
Less than 12 months |  |
Gross Unrealized Losses | (1,125) | 0
Estimated Fair Value | 413,177 | 0
12 months or more |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
Total |  |
Gross Unrealized Losses | (1,125) | 0
Estimated Fair Value | 413,177 | 0
Other securities |  |
Less than 12 months |  |
Gross Unrealized Losses | (353) | (351)
Estimated Fair Value | 47,401 | 30,441
12 months or more |  |
Gross Unrealized Losses | 0 | 0
Estimated Fair Value | 0 | 0
Total |  |
Gross Unrealized Losses | (353) | (351)
Estimated Fair Value | $ 47,401 | $ 30,441

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- Definition Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, 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 326 -SubTopic 30 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=124269663&loc=SL82922890-210455 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27337-111563 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=121590138&loc=SL82922954-210456 + Details
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