Share-based Compensation - Summary of Non-cash, Share-based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	$ 458	$ 576
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	169	167
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	$ 289	$ 409