Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - 2016 Employee Stock Purchase Plan - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 835	$ 401
Research and Development
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	323	110
General and Administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 512	$ 291