Major Category of Assets Measured at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring $ in Thousands	Jun. 30, 2017 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	$ 97,607
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	94,863
Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	2,744
Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	94,863
Quoted prices in active markets for identical assets (Level 1) | Money market funds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	94,863
Significant other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	2,744
Significant other observable inputs (Level 2) | Corporate and other debt securities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Assets	$ 2,744