Stockholders' Equity (Tables)
 3 Months Ended
Mar. 31, 2015
Summary of Stock Option Activity

The following table summarizes the stock option activity (in thousands, except per share amounts):

 

     Shares     Weighted Average
Option Exercise Price
Per Share		      Weighted Average
Grant Date Fair
Value Per Share		      Aggregate
Intrinsic Value		  

Outstanding as of December 31, 2014

      10,411      $ 7.32         

Granted

      292      $ 30.76       $ 13.25      

Exercised

      (1,575 )    $ 7.64          $ 34,624   

Forfeited

      (15 )    $ 23.00         
  

 

 

          

Outstanding as of March 31, 2015

   9,113    $ 7.99    $ 187,935   
  

 

 

          

Exercisable at March 31, 2015

   7,319    $ 7.53    $ 153,764   

Expected to vest

   1,790    $ 9.83    $ 34,132   

Summary of Exercise Price

The exercise prices of outstanding options at March 31, 2015 were in the following ranges:

 


     Options Outstanding      Options Exercisable  

Range of Exercise Prices

    Shares 
(in thousands)		      Weighted Average
Remaining
Contractual Life 
(in years)		      Weighted Average
Exercise Price Per
Share		      Shares 
(in thousands)		      Weighted Average
Exercise Price Per
Share		  

$2.96 to $5.35

      821         3.0       $ 3.66         821       $ 3.66   

$5.36 to $5.67

      837         6.8       $ 5.57         499       $ 5.57   

$5.68 to $8.54

      5,005         5.8       $ 5.74         3,849       $ 5.74   

$8.55 to $8.90

      1,548         5.0       $ 8.65         1,548       $ 8.65   

$8.91 to $23.00

      602         8.9       $ 23.00         602       $ 23.00   

$23.01 to $30.76

      300         9.9       $ 30.55         —         $ —     
  

 

 

           

 

 

     

$2.96 to $30.76

   9,113      5.9    $ 7.99      7,319    $ 7.53   
  

 

 

           

 

 

     
Summary of Weighted Average Assumptions Used to Estimate Fair Value of Stock Option

The following table presents the weighted average assumptions used to estimate the fair value of stock option awards granted.

 

     Three Months Ended  
     March 31,  
     2015     2014  

Expected option term (in years)

      6.0        5.0   

Risk-free interest rate

      1.6 %      1.5 % 

Expected volatility

      43.0 %      45.0 % 

Expected dividend yield

      —   %      —   % 

Weighted average exercise price

    $ 30.76      $ 23.00   

Weighted average fair value at grant date

    $ 13.25      $ 9.40   

Performance Share Units (PSUs) [Member]  
Summary of PSU activity

The following table summarizes the PSU activity (in thousands, except per share data):

 

     Performance
Share Units		      Weighted Average
Grant Date Fair
Value Per Share		  

Outstanding and non-vested as of December 31, 2014

      —         $ —     

Granted

      184       $ 30.76   

Forfeited

      —           —     
  

 

 

     

Outstanding and non-vested as of March 31, 2015

   184    $ 30.76   
  

 

 

     
Restricted Stock Units (RSUs) [Member]  
Summary of RSU activity

The following table summarizes the RSU activity (in thousands, except per share data):

 

     Restricted
Stock Units		      Weighted Average
Grant Date Fair
Value Per Share		  

Outstanding and non-vested as of December 31, 2014

      372       $ 22.99   

Granted

      980       $ 30.76   

Vested and shares issued

      (3 )     $ 18.25   

Forfeited

      (14 )     $ 25.00   
  

 

 

     

Outstanding and non-vested as of March 31, 2015

   1,335    $ 28.68