Share/Stock-Based Compensation - Summary of Share/Stock-Based Compensation Expense (Details) - 2016 Employee Stock Purchase Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total share/stock-based compensation expense	$ 2,492	$ 1,221	$ 427
Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total share/stock-based compensation expense			340
Research and Development | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total share/stock-based compensation expense	961	389	101
Research and Development | Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total share/stock-based compensation expense			340
General and Administrative | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total share/stock-based compensation expense	$ 1,531	$ 832	$ 326