Fair Value of Financial Assets and Liabilities - Summary of Assets and Liabilities Measured at Fair Value on Recurring Basis and Indicate Level of Fair Value Hierarchy Utilized (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Assets:
Cash equivalents	$ 54,423
Available for sale securities	36,098	$ 17,014
Assets Fair Value Disclosure	90,521
Level 2 [Member]
Assets:
Cash equivalents	54,423
Available for sale securities	36,098	$ 17,014
Assets Fair Value Disclosure	$ 90,521