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v3.23.3

Marketable Securities (Tables) | 12 Months Ended
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Sep. 30, 2023
Investments, Debt and Equity Securities [Abstract] |
Summary of amortized cost and fair value | The following is a summary of the amortized cost and the fair value, including accrued interest receivable, as well as unrealized gains (losses) on the short-term and long-term marketable securities as of September 30, 2023 and 2022 (in thousands):
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ |  | ​ |  | Gross |  | Gross |  | ​
​ | ​ | Amortized | ​ | Unrealized | ​ | Unrealized | ​ | ​
​ | ​ | Cost | ​ | Losses | ​ | Gains | ​ | Fair Value
September 30, 2023: |  | ​ |  |  | ​ |  |  | ​ |  |  | ​ |
U.S. Treasury securities and obligations of U.S. government agencies |  | $ | 227,804 | ​ | $ | (2,573) | ​ | $ | — |  | $ | 225,231
Bank certificates of deposits | ​ | ​ | 8,122 | ​ | ​ | (170) | ​ | ​ | — | ​ | ​ | 7,952
Corporate securities | ​ | ​ | 221,155 | ​ | ​ | (4,127) | ​ | ​ | — | ​ | ​ | 217,028
Municipal securities |  | ​ | — | ​ | ​ | — | ​ | ​ | — |  | ​ | —
​ | ​ | $ | 457,081 | ​ | $ | (6,870) | ​ | $ | — | ​ | $ | 450,211
September 30, 2022: | ​ | ​ |  | ​ |  |  | ​ |  |  | ​ |  |
U.S. Treasury securities and obligations of U.S. government agencies | ​ | $ | 804,774 |  | $ | (6,163) |  | $ | 21 | ​ | $ | 798,632
Bank certificates of deposits | ​ | ​ | 8,335 | ​ | ​ | (158) | ​ | ​ | 1 | ​ | ​ | 8,178
Corporate securities | ​ | ​ | 406,270 | ​ | ​ | (8,113) | ​ | ​ | — | ​ | ​ | 398,157
Municipal securities | ​ |  | 59,043 | ​ | ​ | (226) | ​ | ​ | — |  | ​ | 58,817
​ | ​ | $ | 1,278,422 | ​ | $ | (14,660) | ​ | $ | 22 | ​ | $ | 1,263,784
​
Schedule of fair values of marketable securities by contractual maturities | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Amortized | ​ | ​ | ​
​ | ​ | Cost | ​ | ​ | Fair Value
Due in one year or less | ​ | $ | 342,901 | ​ | $ | 338,873
Due after one year through five years | ​ |  | 111,121 | ​ |  | 108,279
Due after five years through ten years | ​ | ​ | — | ​ | ​ | —
Due after ten years | ​ |  | 3,059 | ​ |  | 3,059
Total marketable securities | ​ | $ | 457,081 | ​ | $ | 450,211

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- Definition Tabular disclosure of maturities of an entity's investments as well as any other information pertinent to the investments. + References No definition available. + Details
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- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
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