Stockholders' Equity (Details)	1 Months Ended		12 Months Ended
	Jan. 31, 2016 USD ($) $ / shares shares	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) vote $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares shares	May 31, 2017 USD ($)	Jan. 31, 2017 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
Total shares of common stock sold (in shares)			23,320,551	22,013,644
Share price (in dollars per share) | $ / shares			$ 33.89
Proceeds from follow-on offering | $			$ 0	$ 61,822,000	$ 9,657,000
Number of shares available for future issuance under the plan (in shares)			8,170,939	7,927,394
2016 Inducement Plan
Shareholders' Equity
Number of shares available for future issuance under the plan (in shares)							900,000	450,000
Employee Stock Purchase Plan
Shareholders' Equity
Number of shares available for future issuance under the plan (in shares)			693,856	532,849
Cowen and Company, LLC
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%
Controlled Equity Offering
Shareholders' Equity
Common stock shares sold (in shares)				0	509,741
Share price (in dollars per share) | $ / shares					$ 20.04
Proceeds from follow-on offering | $					$ 9,700,000
Value of shares authorized (up to) | $		$ 25,000,000
Controlled Equity Offering | Cantor
Shareholders' Equity
Commission of sale proceeds		3.00%
Stock options
Shareholders' Equity
Number of shares available for future issuance under the plan (in shares)			5,564,635	5,483,557
Stock options | 2014 Equity Incentive Plan
Shareholders' Equity
Authorized for future issuance (in shares)			1,723,733	1,576,926
Stock options | 2016 Inducement Plan
Shareholders' Equity
Authorized for future issuance (in shares)			188,715	334,062
Common Stock
Shareholders' Equity
Common stock shares sold (in shares)	2,875,000			2,875,000
Share price (in dollars per share) | $ / shares	$ 23.00
Proceeds from follow-on offering | $	$ 61,800,000
Common Stock | Stock options | Over-Allotment Option
Shareholders' Equity
Common stock shares sold (in shares)	375,000