Disclosure of Fair Value of Financial Instruments - Summary of Financial Assets Measured and Recorded at Fair Value on Recurring Basis (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2018	Mar. 31, 2018
Assets:
Total assets	$ 48,049	$ 69,014
Money Market Funds [Member]
Assets:
Total assets	6,091	10,143
U.S. Treasury Securities [Member]
Assets:
Total assets	3,001	2,990
Non-U.S. Government Securities [Member]
Assets:
Total assets	2,999	5,996
Corporate Securities [Member]
Assets:
Total assets	35,958	49,885
Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs) [Member]
Assets:
Total assets	6,091	10,143
Quoted Prices in Active Markets for Identical Assets (Level 1 Inputs) [Member] | Money Market Funds [Member]
Assets:
Total assets	6,091	10,143
Significant Other Observable Inputs (Level 2 Inputs) [Member]
Assets:
Total assets	41,958	58,871
Significant Other Observable Inputs (Level 2 Inputs) [Member] | U.S. Treasury Securities [Member]
Assets:
Total assets	3,001	2,990
Significant Other Observable Inputs (Level 2 Inputs) [Member] | Non-U.S. Government Securities [Member]
Assets:
Total assets	2,999	5,996
Significant Other Observable Inputs (Level 2 Inputs) [Member] | Corporate Securities [Member]
Assets:
Total assets	$ 35,958	$ 49,885