Stockholders' Equity (Tables)
 12 Months Ended
Dec. 31, 2015
Equity [Abstract]  
Schedule of assumptions used for fair value of warrants
The fair value of the warrants was based on the following assumptions using the Black-Scholes option-pricing model:
 
Year Ended December 31,
 
2015
 
2014
 
2013
Risk-free interest rate
1.51
%
to
2.03
%
 
0.02
%
to
2.33
%
 
0.29
%
to
0.52
%
Contractual life (years)
6.3

to
7.2

 
0.3

to
8.0

 
2.0

to
2.9

Expected volatility
47.8
%
to
54.2
%
 
48.5
%
to
57.5
%
 
47.4
%
to
52.8
%
Dividend yield
—
 
 
—
 
 
—
 
Schedule of reserve for unissued shares of common stock
The amount of such shares of the Company’s common stock reserved for these purposes at December 31, 2015 is as follows:
 
Number of Shares
Outstanding stock options
24,277,901

Outstanding restricted stock units
3,747,340

Outstanding common stock warrants
1,631,478

Additional shares available for grant under equity plan
3,095,368

Total
32,752,087