Earnings Per Share (Tables)
 6 Months Ended
Jun. 30, 2015
Earnings Per Share [Abstract]  
Summary of anti-dilutive securities which are excluded from the calculation of weighted average common shares outstanding
The following securities have been excluded from the calculation of weighted-average common shares outstanding because the effect is anti-dilutive for the three and six months ended June 30:  
 
Three Months
Ended June 30,
 
Six Months
Ended June 30,
 
2014
 
2015
 
2014
 
2015
Convertible preferred stock:
 
 
 
 
 
 
 
Series A
2,383,745

 
—

 
2,383,745

 
—

Series B
3,649,368

 
—

 
3,649,368

 
—

Series C
5,406,501

 
—

 
5,406,501

 
—

Series D
3,409,210

 
—

 
3,409,210

 
—

Common stock subject to repurchase
6,166

 
—

 
6,166

 
—

Lender Warrants and Additional Lender Warrant to purchase common stock
100,000

 
200,000

 
100,000

 
200,000

ESPP
—

 
141,806

 
—

 
141,806

Stock options
3,462,243

 
3,384,540

 
3,462,243

 
3,384,540