Cash, Cash Equivalents, and Marketable Securities - Schedule of Unrealized Positions for Held-to-Maturity Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Mar. 31, 2026
Cash, Cash Equivalents, and Marketable Securities [Line Items]
U.S. Treasury securities, available-for-sale, Amortized Cost	$ 2,581,603	$ 2,876,156
U.S. Treasury securities, available-for-sale, Gross Unrealized Gains	27	538
U.S. Treasury securities, available-for-sale, Gross Unrealized Losses	(16,310)	(4,093)
U.S. Treasury securities, available-for-sale, Fair Value	2,565,320	2,872,601
Accrued interest receivable	21,600	19,600
U.S. Treasury securities
Cash, Cash Equivalents, and Marketable Securities [Line Items]
U.S. Treasury securities, available-for-sale, Amortized Cost	1,891,260	2,125,053
U.S. Treasury securities, available-for-sale, Gross Unrealized Gains	0	538
U.S. Treasury securities, available-for-sale, Gross Unrealized Losses	(11,938)	(1,412)
U.S. Treasury securities, available-for-sale, Fair Value	1,879,322	2,124,179
Corporate bonds
Cash, Cash Equivalents, and Marketable Securities [Line Items]
U.S. Treasury securities, available-for-sale, Amortized Cost	672,769	751,103
U.S. Treasury securities, available-for-sale, Gross Unrealized Gains	25	0
U.S. Treasury securities, available-for-sale, Gross Unrealized Losses	(4,362)	(2,681)
U.S. Treasury securities, available-for-sale, Fair Value	668,432	748,422
Commercial paper
Cash, Cash Equivalents, and Marketable Securities [Line Items]
U.S. Treasury securities, available-for-sale, Amortized Cost	17,574
U.S. Treasury securities, available-for-sale, Gross Unrealized Gains	2
U.S. Treasury securities, available-for-sale, Gross Unrealized Losses	(10)
U.S. Treasury securities, available-for-sale, Fair Value	$ 17,566	$ 0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 30
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479130/326-30-45-1

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
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-Paragraph 1
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Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 210
-SubTopic 10
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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