Investable Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Mar. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	$ 915,660	$ 770,998
Gross Unrealized Gains	37	1,443
Gross Unrealized Losses	7,906	74
Fair Market Value	907,791	772,367
Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	61,916	157,297
Gross Unrealized Gains	0	0
Gross Unrealized Losses	3	0
Fair Market Value	61,913	157,297
Repurchase Agreement
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value		33,000
Repurchase Agreement | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost		33,000
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Market Value		33,000
Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	628,200	350,379
Gross Unrealized Gains	37	623
Gross Unrealized Losses	2,448	17
Fair Market Value	625,789	350,985
Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	225,544	263,322
Gross Unrealized Gains	0	820
Gross Unrealized Losses	5,455	57
Fair Market Value	220,089	264,085
Money Market Funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value	32,955	124,297
Money Market Funds | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	32,955	124,297
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Market Value	32,955	124,297
Commercial Paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Market Value	28,958
Commercial Paper | Cash Equivalents
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	28,961
Gross Unrealized Gains	0
Gross Unrealized Losses	3
Fair Market Value	28,958
Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	148,128	45,237
Gross Unrealized Gains	0	1
Gross Unrealized Losses	397	3
Fair Market Value	147,731	45,235
U.S. Treasury mutual fund securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	287,010	72,221
Gross Unrealized Gains	0	28
Gross Unrealized Losses	1,384	0
Fair Market Value	285,626	72,249
U.S. Treasury mutual fund securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	89,168
Gross Unrealized Gains	0
Gross Unrealized Losses	1,796
Fair Market Value	87,372
Government-backed securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	131,954	128,668
Gross Unrealized Gains	1	13
Gross Unrealized Losses	554	12
Fair Market Value	131,401	128,669
Government-backed securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	126,150	225,231
Gross Unrealized Gains	0	190
Gross Unrealized Losses	3,378	37
Fair Market Value	122,772	225,384
Corporate Debt Securities | Short-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	61,108	104,253
Gross Unrealized Gains	36	581
Gross Unrealized Losses	113	2
Fair Market Value	61,031	104,832
Corporate Debt Securities | Long-term Investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	10,226	38,091
Gross Unrealized Gains	0	630
Gross Unrealized Losses	281	20
Fair Market Value	$ 9,945	$ 38,701