Stockholders' Equity (Details)		9 Months Ended
	Jan. 06, 2016 USD ($) $ / shares shares	Sep. 30, 2017 USD ($) vote shares	Sep. 30, 2016 USD ($)	May 31, 2017 USD ($)	Jan. 31, 2017 shares	Dec. 31, 2016 shares	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 | $		$ 0	$ 61,822,000
Total common stock reserved for future issuance (in shares)		8,775,213				7,927,394
Cowen
Shareholders' Equity
At-the-market offering, aggregate offering price (up to) | $				$ 50,000,000.0
At-the-market offering, commission as a percentage of gross proceeds (up to)				3.00%
2016 Inducement Plan
Shareholders' Equity
Total common stock reserved for future issuance (in shares)					900,000		450,000
Employee Stock Purchase Plan
Shareholders' Equity
Total common stock reserved for future issuance (in shares)		718,210				532,849
Stock options
Shareholders' Equity
Total common stock reserved for future issuance (in shares)		5,926,814				5,483,557
Stock options | 2014 Equity Incentive Plan
Shareholders' Equity
Authorized for future issuance (in shares)		1,700,824				1,576,926
Stock options | 2016 Inducement Plan
Shareholders' Equity
Authorized for future issuance (in shares)		429,365				334,062
Common Stock
Shareholders' Equity
Sale of shares under the sales agreement (in shares)	2,875,000
Share price (in dollars per share) | $ / shares	$ 23
Net proceeds from follow-on public offering | $	$ 61,800,000
Common Stock | Stock options | Over-Allotment Option
Shareholders' Equity
Sale of shares under the sales agreement (in shares)	375,000