Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 593,589	$ 472,484
Contingent consideration	9,000	9,575
Cross-currency swap
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative fair value	3,786
Repurchase Agreement
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	20,000	20,000
Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	250,775	370,677
Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	207,795	21,718
Shockwave Medical
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	55,704	56,195
Money Market Funds
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	115,019	60,089
Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	32,831	56,795
Level 1 | Shockwave Medical
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	55,704	56,195
Level 1 | Money Market Funds
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	115,019	60,089
Level 2 | Cross-currency swap
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative fair value	3,786
Level 2 | Repurchase Agreement
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	20,000	20,000
Level 2 | Commercial Paper | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	32,831	56,795
Level 3
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration	9,000	9,575
Government-backed securities | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	67,995	126,381
Government-backed securities | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	91,064
Government-backed securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	67,995	126,381
Government-backed securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	91,064
U.S. Treasury securities | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	42,648	58,787
U.S. Treasury securities | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure		21,718
U.S. Treasury securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	42,648	58,787
U.S. Treasury securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure		21,718
Corporate Debt Securities | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	107,301	128,714
Corporate Debt Securities | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	116,731	21,718
Corporate Debt Securities | Level 2 | Short-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	107,301	$ 128,714
Corporate Debt Securities | Level 2 | Long-term Investments
Fair Value, Assets and Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 116,731