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v3.23.3

Investments (Adjusted cost and estimated market value of available-for-sale investments) (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Mar. 31, 2023
--- | --- | ---
Available-for-sale securities, amortized cost: |  |
Amortized cost | $ 2,758,446 | $ 3,006,587
Available-for-sale securities, fair value: |  |
Available for sale investments, estimated market value | 2,472,128 | 2,709,037
US Treasury Securities [Member] |  |
Available-for-sale securities, amortized cost: |  |
Due in one year or less | 251,106 | 354,875
Due after one year through five years | 599,626 | 754,175
Due after five years through ten years | 659,400 | 736,089
Due after ten years | 733,486 | 790,568
Amortized cost | 2,243,618 | 2,635,707
Available-for-sale securities, fair value: |  |
Due in one year or less | 249,366 | 354,184
Due after one year through five years | 569,012 | 717,552
Due after five years through ten years | 590,567 | 665,708
Due after ten years | 612,788 | 654,201
Available for sale investments, estimated market value | 2,021,733 | 2,391,645
Mortgage-backed securities [Member] |  |
Available-for-sale securities, amortized cost: |  |
Amortized cost | 514,679 | 370,880
Available-for-sale securities, fair value: |  |
Available for sale investments, estimated market value | $ 450,248 | $ 317,392

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