Financial Instruments Measured at Fair Value (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Mar. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	$ 164,822	$ 123,553
Contingent consideration	7,563	6,510
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration	7,563	6,510
US Treasury mutual fund Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	45,656	19,487
US Treasury mutual fund Securities | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, fair value disclosure	45,656	19,487
US Government-sponsored Enterprises 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	118,166	90,070
US Government-sponsored Enterprises 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	1,000	13,996
US Government-sponsored Enterprises 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	118,166	90,070
US Government-sponsored Enterprises 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	$ 1,000	$ 13,996