Share-based Compensation - Summary of Non-cash, Share-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	$ 119	$ 267	$ 339	$ 605
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	44	94	124	189
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total expenses	$ 75	$ 173	$ 215	$ 416