Fair Value Measurements - Information about financial assets measured at fair value on recurring basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands	Dec. 31, 2021	Mar. 31, 2021
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 679,618	$ 682,522
Cash and cash equivalents:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	139,891	101,626
Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	533,952	575,254
Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	5,775	5,642
Money market funds | Cash and cash equivalents:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	139,891	101,626
Money market funds | Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	5,775	5,642
Certificates of deposit | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	93,720	48,099
Commercial paper | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	32,049	11,681
Corporate notes and bonds | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	88,864	39,873
U.S. treasury securities | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	319,319	475,601
Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	464,985	582,869
Level 1 | Money market funds | Cash and cash equivalents:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	139,891	101,626
Level 1 | Money market funds | Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	5,775	5,642
Level 1 | Certificates of deposit | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 1 | Commercial paper | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 1 | Corporate notes and bonds | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 1 | U.S. treasury securities | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	319,319	475,601
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	214,633	99,653
Level 2 | Money market funds | Cash and cash equivalents:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 2 | Money market funds | Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 2 | Certificates of deposit | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	93,720	48,099
Level 2 | Commercial paper | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	32,049	11,681
Level 2 | Corporate notes and bonds | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	88,864	39,873
Level 2 | U.S. treasury securities | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | Money market funds | Cash and cash equivalents:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | Money market funds | Restricted cash
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | Certificates of deposit | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | Commercial paper | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | Corporate notes and bonds | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	0	0
Level 3 | U.S. treasury securities | Short-term investments:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets fair value	$ 0	$ 0