Fair Value Measurements - Information about Financial Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring - USD ($) $ in Thousands | Jun. 30, 2018 | Mar. 31, 2018 |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | $ 651,278 | $ 192,007 |
Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 477,015 | 68,364 |
Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 166,061 | 115,441 |
Restricted cash | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 8,202 | 8,202 |
Money market funds | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 466,925 | 38,458 |
Commercial paper | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 10,090 | 21,710 |
Commercial paper | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 41,668 | 21,699 |
Certificates of deposit | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 22,153 | 20,492 |
Corporate notes and bonds | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 14,438 | 9,794 |
U.S. treasury securities | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 2,698 |
U.S. treasury securities | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 54,531 | 40,187 |
U.S. government agencies | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 5,498 |
U.S. government agencies | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 33,271 | 23,269 |
Money market funds | Restricted cash | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 8,202 | 8,202 |
Level 1 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 529,658 | 89,545 |
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 | 466,925 | 38,458 |
Level 1 | Commercial paper | Cash and cash equivalents | | |
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 | 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 | 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 | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 2,698 |
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 | 54,531 | 40,187 |
Level 1 | U.S. government agencies | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 0 |
Level 1 | U.S. government agencies | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 0 | 0 |
Level 1 | Money market funds | Restricted cash | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 8,202 | 8,202 |
Level 2 | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 121,620 | 102,462 |
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 | Commercial paper | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 10,090 | 21,710 |
Level 2 | Commercial paper | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 41,668 | 21,699 |
Level 2 | Certificates of deposit | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 22,153 | 20,492 |
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 | 14,438 | 9,794 |
Level 2 | U.S. treasury securities | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 0 |
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 2 | U.S. government agencies | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 5,498 |
Level 2 | U.S. government agencies | Short-term investments | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | 33,271 | 23,269 |
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 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 | Commercial paper | Cash and cash equivalents | | |
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 | 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 | 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 | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 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 |
Level 3 | U.S. government agencies | Cash and cash equivalents | | |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | | |
Assets fair value | | 0 |
Level 3 | U.S. government agencies | Short-term investments | | |
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 |