Net Loss Per Share (Tables)
 12 Months Ended
Dec. 31, 2015
Earnings Per Share [Abstract]  
Schedule of computation of basic and diluted net loss per share attributable to common stockholders
The following table sets forth the computation of basic and diluted net loss per share attributable to common stockholders during the years ended December 31, 2015, 2014 and 2013 (in thousands, except per share data):
 
Year Ended December 31,
 
2015
 
2014
 
2013
Net loss
$
(64,911
)
 
$
(48,429
)
 
$
(25,056
)
Weighted-average common shares outstanding
81,914

 
70,837

 
58,540

Net loss per share — basic and diluted
$
(0.79
)
 
$
(0.68
)
 
$
(0.43
)
Schedule of anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders
The following table presents the number of anti-dilutive shares excluded from the calculation of diluted net loss per share attributable to common stockholders at December 31, 2015, 2014 and 2013 (in thousands):
 
December 31,
 
2015
 
2014
 
2013
Options to purchase common stock
24,278

 
25,590

 
18,363

Common stock warrants
1,631

 
3,926

 
5,931

Conversion of convertible preferred stock
—

 
—

 
2,857

Unvested restricted stock awards
3,747

 
828

 
55

Total shares excluded from net loss per share attributable to common stockholders
29,656

 
30,344

 
27,206