Employee Stock and Benefit Plans (Tables)
 12 Months Ended
Dec. 31, 2014
Share-based Compensation, Allocation and Classification in Financial Statements [Abstract]  
Summary of Stock Option Activity Under All Plans
The following table summarizes stock option activity for the year ended December 31, 2014:
 
Number of
Options
 
Weighted Average
Exercise Price
per Option
 
Weighted Average
Remaining Life
 
Aggregate Intrinsic
Value
Outstanding, December 31, 2013
11,259,868

 
$
36.20

 
 

 
 

Granted
1,752,921

 
0.86

 
 

 
 

Exercised
—

 
—

 
 

 
 

Forfeited
(6,978,638
)
 
35.63

 
 

 
 

Outstanding, December 31, 2014
6,034,151

 
26.57

 
5.71

 
$
—

Exercisable, December 31, 2014
3,996,673

 
38.55

 
4.04

 
—
Assumptions in Option Pricing Model
The weighted average fair value of the stock option awards on their grant dates using the Black-Scholes-Merton option-pricing model was less than $0.01 for each option granted during the year ended December 31, 2014, $4.64 for each option granted during the year ended December 31, 2013 and $7.31 for each option granted during the year ended December 31, 2012 based on the following assumptions:
 
2014
 
2013
 
2012
Risk free interest rate
1.60% - 1.63%
 
0.63% - 1.49%
 
0.62% - 0.95%
Expected stock price volatility
69.53% - 96.99%
 
56.56% - 69.53%
 
50.00% - 56.56%
Expected term in years
4.78 - 4.81
 
4.78 - 4.81
 
4.65 - 4.78
Expected dividend yield
—
 
—
 
—
Summary of the Status of Non-Vested Restricted Stock Awards
Following is a summary of our restricted stock:
 
Number of
Shares
 
Weighted Average
Grant Date
Fair Value
Per Share
Restricted stock awards as of December 31, 2013
3,919,485

 
$12.99
Granted
3,605,538

 
0.85
Vested
(1,140,667
)
 
16.80
Forfeited
(2,294,608
)
 
7.69
Restricted stock awards as of December 31, 2014
4,089,748

 
3.75