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	Jun. 30, 2018	Dec. 31, 2017
Assets:
Cash Equivalents	$ 749
Available-for-sale securities	16,935	$ 17,014
Total	17,684
Level 2 [Member]
Assets:
Cash Equivalents	749
Available-for-sale securities	16,935	$ 17,014
Total	$ 17,684