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Fair Value Measurements - Securities in Unrealized Loss Positions (Details) $ in Thousands | Dec. 31, 2021 USD ($) security | Sep. 30, 2021 USD ($) security
--- | --- | ---
Debt Securities, Available-for-sale [Line Items] |  |
Number of debt securities with unrealized loss | security | 36 | 31
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | $ (987) | $ (1,584)
12 months or more, unrealized gross losses | (2,920) | (1,056)
Total unrealized gross losses | (3,907) | (2,640)
Less than 12 months, fair value | 141,842 | 52,397
12 months or more, fair value | 140,156 | 102,324
Total, fair value | 281,998 | 154,721
Held-to-maturity securities |  |
Less than 12 months, unrealized gross losses | 0 | 0
Less than 12 months, fair value | 0 | 0
12 months or more, unrealized gross losses | 0 | 0
12 months or more, fair value | 0 | 0
Total unrealized gross losses | 0 | 0
Total, fair value | 0 | 0
Less than 12 months, unrealized gross losses | (987) | (1,584)
Less than 12 months, fair value | 141,842 | 52,397
12 months or more, unrealized gross losses | (2,920) | (1,056)
12 months or more, fair value | 140,156 | 102,324
Total unrealized gross losses | (3,907) | (2,640)
Total fair value | 281,998 | 154,721
U.S. government and agency securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (88) |
12 months or more, unrealized gross losses | 0 |
Total unrealized gross losses | (88) |
Less than 12 months, fair value | 13,970 |
12 months or more, fair value | 0 |
Total, fair value | 13,970 |
Asset-backed securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (144) | (15)
12 months or more, unrealized gross losses | (855) | (614)
Total unrealized gross losses | (999) | (629)
Less than 12 months, fair value | 71,099 | 4,639
12 months or more, fair value | 87,409 | 70,058
Total, fair value | 158,508 | 74,697
Mortgage-backed securities |  |
Available-for-sale securities |  |
Less than 12 months, unrealized gross losses | (755) | (1,569)
12 months or more, unrealized gross losses | (2,065) | (442)
Total unrealized gross losses | (2,820) | (2,011)
Less than 12 months, fair value | 56,773 | 47,758
12 months or more, fair value | 52,747 | 32,266
Total, fair value | $ 109,520 | $ 80,024

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