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Stockholders' Equity (Details)
 1 Months Ended 12 Months Ended
Nov. 30, 2016
USD ($)
$ / shares
shares
May 31, 2015
USD ($)
Apr. 30, 2015
USD ($)
$ / shares
shares
Dec. 31, 2016
USD ($)
vote
$ / shares
shares
Dec. 31, 2015
USD ($)
$ / shares
shares
Dec. 31, 2014
USD ($)
Common Stock            
Authorized shares of common stock       125,000,000 125,000,000  
Par value of shares of common stock (in dollars per share) | $ / shares       $ 0.001 $ 0.001  
Number of votes for each share of stock | vote       1    
Dividends declared | $       $ 0    
Options issued and outstanding (in shares)       5,251,832 4,179,521  
Shares available for issuance       887,724 1,058,359  
Total number of shares reserved for issuance       6,748,609 5,987,880  
Common stock, shares issued       33,762,278 27,685,291  
Net proceeds from sale of common stock in private placement | $       $ 0 $ 37,258,000 $ 0
Options            
Common Stock            
Options issued and outstanding (in shares)       5,251,832 4,179,521  
Shares available for issuance       887,724 1,058,359  
ESPP            
Employee Stock Purchase Plan            
Maximum offering period   12 months        
Purchase period   6 months        
Maximum fair market value of shares an employee can purchase per calendar year | $   $ 25,000        
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model            
Weighted-average volatility, low end of range (as a percent)       46.38% 53.57%  
Weighted-average volatility, high end of range (as a percent)       75.72% 58.10%  
Risk-free interest rate, low end of range (as a percent)       0.40% 0.17%  
Risk-free interest rate, high end of range (as a percent)       0.50% 0.33%  
ESPP | Minimum            
Employee Stock Purchase Plan            
Minimum purchase price as a percentage of fair market value   85.00%        
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model            
Weighted-average expected term       6 months 5 months 27 days  
ESPP | Maximum            
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model            
Weighted-average expected term       1 year 11 months 27 days  
Common Stock            
Common Stock            
Common stock, shares issued 5,723,300          
Shares issued, price per share (in usd per share) | $ / shares $ 6.00          
Sale of stock, consideration received on transaction, gross | $ $ 34,300,000          
Proceeds from issuance of common stock | $ 32,100,000          
Payments of stock issuance costs | $ $ 2,200,000          
Number of common stock issued and sold in private placement       5,723,300 4,907,975  
Share Price (in usd per share) | $ / shares       $ 7.74 $ 7.20  
Common Stock | Private placement            
Common Stock            
Number of common stock issued and sold in private placement     4,907,975      
Share Price (in usd per share) | $ / shares     $ 8.15      
Gross proceeds from sale of common stock in private placement | $     $ 40,000,000      
Net proceeds from sale of common stock in private placement | $     37,300,000      
Agent fees and other expenses | $     $ 2,700,000      
Common Stock | ESPP            
Common Stock            
Shares available for issuance       609,053 750,000  
Prepaid Expenses and Other Current Assets            
Common Stock            
Accounts receivable | $       $ 200,000