Fair Value Measurement - Cash And Cash Equivalents And Available For Sale Securities At Fair Value (Detail) - USD ($) $ in Thousands	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Fair value measurement
Cash And Cash Equivalents At Amortized Cost	$ 465,829	$ 93,667
Available-for-sale Securities, Amortized Cost Basis	12,033	196,320
Cash And Cash Equivalents And Short Term Investments Amortized Cost	477,862	289,987
Available-for-sale Securities, Gross Unrealized Gain	1	15
Available for sale Securities Gross Unrealized Gain Loss	1	15
Cash and Cash Equivalents, at Carrying Value	465,829	93,667
Short-term Investments	12,034	196,335
Cash, Cash Equivalents, and Short-term Investments	$ 477,863	$ 290,002

Available for sale Securities Gross Unrealized Gain Loss

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- Definition

Cash And Cash Equivalents And Short Term Investments Amortized Cost.

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Cash And Cash Equivalents At Amortized Cost

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
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Amount of unrealized gain on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

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Cash includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the customer may deposit additional funds at any time and effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid Investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months. Short-term investments, exclusive of cash equivalents, generally consist of marketable securities intended to be sold within one year (or the normal operating cycle if longer) and may include trading securities, available-for-sale securities, or held-to-maturity securities (if maturing within one year), as applicable.

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Amount of investments including trading securities, available-for-sale securities, held-to-maturity securities, and short-term investments classified as other and current.

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