Stockholders' Equity (Details)	1 Months Ended	6 Months Ended
	Jan. 31, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) vote shares	Jun. 30, 2017 USD ($)	Dec. 31, 2017 shares	Nov. 30, 2017 shares	May 31, 2017 USD ($)	Mar. 31, 2016 shares
Shareholders' Equity
Authorized shares of common stock (in shares)		100,000,000		100,000,000
Dividends declared | $		$ 0
Number of votes per share | vote		1
Net proceeds from follow-on public offering | $		$ 134,268,000	$ 0
Total common stock reserved for future issuance (in shares)		9,373,075		8,170,939
2016 Inducement Plan
Shareholders' Equity
Total common stock reserved for future issuance (in shares)					1,350,000		450,000
Cowen
Shareholders' Equity
At-the-market offering, aggregate offering price (up to) | $						$ 50,000,000
At-the-market offering, commission as a percentage of gross proceeds (up to)						3.00%
Employee Stock Purchase Plan
Shareholders' Equity
Total common stock reserved for future issuance (in shares)		892,444		693,856
Stock options
Shareholders' Equity
Total common stock reserved for future issuance (in shares)		6,135,087		5,564,635
Stock options | 2014 Equity Incentive Plan
Shareholders' Equity
Authorized for future issuance (in shares)		1,794,105		1,723,733
Stock options | 2016 Inducement Plan
Shareholders' Equity
Authorized for future issuance (in shares)		551,439		188,715
Common Stock
Shareholders' Equity
Sale of shares under the sales agreement (in shares)	3,450,000
Share price (in dollars per share) | $ / shares	$ 41.50
Net proceeds from follow-on public offering | $	$ 134,300,000
Common Stock | Stock options | Over-Allotment Option
Shareholders' Equity
Sale of shares under the sales agreement (in shares)	450,000