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Equity Incentive Plans - Additional Information (Detail) - USD ($)
 1 Months Ended 12 Months Ended
Jan. 01, 2017
Jan. 01, 2015
Jun. 18, 2014
Jun. 30, 2015
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Nov. 30, 2016
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Vesting period         4 years        
Common stock reserved         1,454,549        
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options     1,153,279            
Number of shares granted during the period         1,524,014 379,709 188,888    
Weighted-average grant-date estimated fair value of options granted         $ 7.69 $ 12.91 $ 18.53    
Estimated fair value of common stock         $ 14.20        
Estimated fair value of options vested during period         $ 6,400,000 $ 2,400,000 $ 500,000    
Estimated fair value of restricted stock vested during period         $ 500,000        
Shares available for future grant         2,206,626 1,644,420 1,265,282   3,914
Stock-based compensation charge             $ 800,000    
Gross proceeds from issuance of common stock       $ 77,800,000          
Proceeds from issuance of common stock, net of issuance costs       $ 74,300,000 $ 190,573,000 $ 74,323,000 $ 61,241,000    
Common stock sold and issued       7,242,992          
Purchase price of common shares       $ 10.70          
Warrants issued to purchase common stock       2,172,899          
Purchase price for warrants       $ 0.125          
Warrants exercise price per share       $ 13.91          
Warrants expiration term       5 years          
Warrants description         The warrants are exercisable for an exercise price of $13.91 per share at any time prior to the earlier of (i) 5 years from the date of issuance or (ii) certain changes in control of the Company.        
Maximum warrants ownership percentage by each holder of warrants       9.99%          
Number of warrants exercised         0 0      
Expected dividend yield         $ 0        
Issuance of common stock for services (Shares)         20,118 13,285 10,000    
Issuance of common stock for services, amount         $ 187,000 $ 194,000 $ 208,000    
Subsequent Event [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options 1,892,376                
Employee Stock Purchase Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unrecognized stock based compensation expense         $ 100,000        
Unrecognized stock based compensation expense, weighted-average remaining recognition period         2 months 12 days        
2014 Equity Incentive Award Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Common stock reserved         1,419,328        
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options         10,683,053        
Possible increase in shares reserved for issuance as percentage of outstanding stock         4.00%        
2008 Stock Incentive Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Common stock reserved         35,221        
2014 Employee Stock Purchase Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Common stock reserved         202,762        
Increase in shares reserved for issuance, maximum shares to be issued up on exercise of stock options   185,892     2,230,374        
Possible increase in shares reserved for issuance as percentage of outstanding stock         1.00%        
Employee stock purchase plan initial offering commenced period         Sep. 01, 2014        
Employee stock purchase plan initial offering ending period         Feb. 27, 2015        
Shares available for future grant         278,020        
Number of shares sold under the plan         69,054 41,580 0    
Weighted-average purchase price         $ 8.34 $ 13.25      
Proceeds from issuance of shares         $ 600,000 $ 600,000      
2016 Employment Commencement Incentive Plan [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of shares granted during the period         0        
2016 Employment Commencement Incentive Plan [Member] | Board of Directors [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Common stock reserved               1,000,000  
Restricted Stock [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Share-based award accelerated vesting number of shares             58,969    
Options to Purchase Common Stock [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unrecognized stock based compensation expense         $ 11,500,000        
Unrecognized stock based compensation expense, weighted-average remaining recognition period         2 years 10 months 24 days        
Non Employee Stock Option [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of shares granted during the period         12,500 5,000 10,000    
Weighted-average grant-date estimated fair value of options granted         $ 13.71 $ 18.58 $ 20.77    
Stock-based compensation charge         $ 100,000 $ 200,000 $ 100,000    
Restricted Stock Units (RSUs) [Member]                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Unrecognized stock based compensation expense         $ 2,100,000        
Unrecognized stock based compensation expense, weighted-average remaining recognition period         3 years 6 months