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Stockholders' Equity - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 2 Months Ended 12 Months Ended
Jan. 01, 2017
Nov. 30, 2017
Oct. 31, 2017
Sep. 30, 2016
May 31, 2015
Apr. 30, 2015
Jul. 31, 2014
May 31, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Shares issued (in shares)                 0 0  
Shares outstanding (in shares)                 0 0  
Proceeds from issuance of common stock   $ 86,600 $ 86,600 $ 30,300       $ 75,400 $ 86,624 $ 30,310 $ 75,359
Stock issuance costs     $ (5,400) $ (2,400)       $ (5,400)      
Shares outstanding (in shares)                 48,068,650 25,413,055  
Common stock reserved for future issuance (in shares)                 5,711,913 4,925,986  
Employee share-based compensation expense                 $ 8,633 $ 9,283 6,297
Intrinsic value of stock options exercised                 $ 868 $ 124 $ 5,000
Employee Stock Option                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Common stock reserved for future issuance (in shares)                 4,094,532 3,590,393  
Unrecognized stock based compensation expense                 $ 10,800    
Weighted average recognition period for stock-based compensation expense                 2 years 25 days    
Restricted stock units                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Common stock reserved for future issuance (in shares)                 195,172 107,250  
Vesting term                   4 years  
Award vesting percent                   25.00%  
Total estimated grant date fair value of RSUs granted                 $ 1,300    
Total fair value of RSUs vested                 150    
Employee share-based compensation expense                 719    
Unrecognized stock based compensation expense                 $ 1,500    
Weighted average recognition period for stock-based compensation expense                 2 years 4 months 6 days    
2014 Employee Stock Purchase Plan | Employee Stock                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Annual increase in common stock available for issuance (as a percent)             1.00%        
Increase in authorized shares             200,000        
Common stock reserved for future issuance (in shares)                 475,010 503,620  
2014 Omnibus Incentive Plan                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Annual increase in common stock available for issuance (as a percent)             4.00%        
Increase in authorized shares 1,016,522                    
Common stock reserved for future issuance (in shares)             1,400,000        
Common stock authorized (in shares)                 3,927,135    
2008 and 2014 Equity Incentive Plans | Employee Stock Option                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Vesting term                 4 years    
Option expiration period                 10 years    
Public Offering                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Stock issued during period (in shares)     22,425,000 5,226,369   3,000,000          
Share price (in dollars per share)     $ 4.1 $ 6.25   $ 26.50          
Underwriters option                      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                      
Stock issued during period (in shares)         47,409            
Share price (in dollars per share)         $ 26.50     $ 26.50