Investments - Cost, Gross Unrealized Gains and Losses, and Fair Value of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Mar. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	$ 679,020	$ 93,107
Gross Unrealized Gains	25	6
Gross Unrealized Losses	(800)	(27)
Fair Value	678,245	93,086
Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	15,105	16,946
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(1)
Fair Value	15,105	16,945
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	663,915	76,161
Gross Unrealized Gains	25	6
Gross Unrealized Losses	(800)	(26)
Fair Value	663,140	76,141
Commercial paper \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost		2,290
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		2,290
Corporate notes and bonds \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost		3,517
Gross Unrealized Gains		0
Gross Unrealized Losses		(1)
Fair Value		3,516
Corporate notes and bonds \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	26,671	46,662
Gross Unrealized Gains	5	3
Gross Unrealized Losses	(32)	(24)
Fair Value	26,644	46,641
Money market funds \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	15,105	9,838
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	15,105	9,838
Certificates of deposit \| Cash and Cash Equivalents
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost		1,301
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		1,301
Certificates of deposit \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	230	4,867
Gross Unrealized Gains	0	1
Gross Unrealized Losses	0	0
Fair Value	230	4,868
Asset-backed securities \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	5,708	3,264
Gross Unrealized Gains	1	0
Gross Unrealized Losses	(5)	(1)
Fair Value	5,704	3,263
Commercial paper \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	499	16,411
Gross Unrealized Gains	9	1
Gross Unrealized Losses	(1)	0
Fair Value	507	16,412
Sovereign bonds \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	8,780	1,100
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(15)	(1)
Fair Value	8,765	1,099
U.S. government and agency securities \| Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Cost or Amortized Cost	622,027	3,857
Gross Unrealized Gains	10	1
Gross Unrealized Losses	(747)	0
Fair Value	$ 621,290	$ 3,858

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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563

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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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
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Amortized cost excluding accrued interest, after 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/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

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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).

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