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Stock Option and Compensation Plans - Narrative (Details) - USD ($)
$ / shares in Units, $ in Thousands
1 Months Ended 12 Months Ended
Jan. 01, 2019
Apr. 30, 2016
Aug. 31, 2013
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Stock Option and Compensation Plans            
Options outstanding (in shares)       5,615,000    
Weighted-average exercise price of options (in dollars per share)       $ 14.17    
Weighted-average remaining contractual life of options       7 years 9 months 18 days    
Share-based compensation expense       $ 11,072 $ 18,171 $ 31,660
Shares issued under ESPP (in shares)       16,358    
ESPP            
Stock Option and Compensation Plans            
Number of shares of common stock available for issuance under the Plan (in shares)       952,229    
Purchase price of common stock as percentage of fair market value   85.00%        
Share-based compensation expense       $ 100 100  
Expected weighted average period to recognize share-based compensation costs       3 months 18 days    
Common stock issued (in shares)       31,413    
Proceeds from stock plans       $ 65    
Restricted stock units            
Stock Option and Compensation Plans            
Share-based compensation expense       $ 300    
RSUs expected to vest (in shares)       550,000    
Weighted-average fair value of RSUs expected to vest (in dollars per share)       $ 10.36    
Aggregate intrinsic value of RSUs expected to vest       $ 700    
Total fair value vested       3,400    
Employees | Stock options            
Stock Option and Compensation Plans            
Share-based compensation expense       7,600 13,100 22,800
Unrecognized share-based compensation costs for option awards, net of estimated forfeitures       $ 9,000    
Expected weighted average period to recognize share-based compensation costs       2 years 1 month 6 days    
Employees | Restricted stock units            
Stock Option and Compensation Plans            
Share-based compensation expense       $ 3,300 4,400 6,900
Expected weighted average period to recognize share-based compensation costs       1 year 9 months 18 days    
Unrecognized compensation costs, net of estimated forfeitures       $ 3,200    
Consultants | Non-employee Options            
Stock Option and Compensation Plans            
Share-based compensation expense       200 $ 300 $ 1,700
Unrecognized share-based compensation costs for option awards, net of estimated forfeitures       $ 200    
Expected weighted average period to recognize share-based compensation costs       1 year 8 months 12 days    
Consultants | Restricted stock units            
Stock Option and Compensation Plans            
Expected weighted average period to recognize share-based compensation costs       1 year    
Unrecognized compensation costs, net of estimated forfeitures       $ 100    
Maximum | ESPP            
Stock Option and Compensation Plans            
Number of shares reserved for issuance under the Plan (in shares)   1,000,000        
2013 Plan            
Stock Option and Compensation Plans            
Number of shares of common stock available for issuance under the Plan (in shares)       840,000    
Annual increase in shares reserved for issuance under the Plan (in shares)     2,542,372      
Annual increase in shares reserved for issuance under the Plan (as a percent)     4.00%      
Increase in number of shares available under the Plan (in shares)       8,554,000    
2013 Plan | Subsequent Event            
Stock Option and Compensation Plans            
Annual increase in shares reserved for issuance under the Plan (as a percent) 4.00%          
Increase in number of shares available under the Plan (in shares) 1,656,000          
2013 Plan | Maximum            
Stock Option and Compensation Plans            
Number of shares reserved for issuance under the Plan (in shares)     3,359,641      
2007 Plan            
Stock Option and Compensation Plans            
Number of shares of common stock available for issuance under the Plan (in shares)     739,317