Commitments and Contingencies - Summary of Future Retainer Payment Due Under Letter Agreement (Detail) - Letter Agreement with Dr. Stelios Papadopoulos [Member] - USD ($) $ in Thousands	Dec. 31, 2017	May 31, 2016
Contingencies And Commitments [Line Items]
2018	$ 840
2019	420
Total	$ 1,260	$ 2,500

Amount of contractual obligation due in the next fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

No definition available.

Name:	us-gaap_ContractualObligationDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant