Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2015
Share-based Compensation [Abstract]  
Summary of Option Activity
A summary of the option activity under the Plans during the six months ended June 30, 2015 is presented below:    
 
 
Options Outstanding
 
 
Shares
 
Weighted Average Exercise Price Per Share
 
Weighted Average Remaining Contractual Term
 
Aggregate Intrinsic Value
 
 
 
 
 
 
(in years)
 
(in thousands)
Balances at December 31, 2014
 
8,515,879

 
$
8.76

 
 
 
 
Options exercised
 
(1,555,909
)
 
8.29

 
 
 
 
Options canceled
 
(10
)
 
9.30

 
 
 
 
Options forfeited
 
(56,715
)
 
16.13

 
 
 
 
Balances at June 30, 2015
 
6,903,245

 
$
8.81

 
6.51
 
$
735,146

Vested and expected to vest at June 30, 2015
 
6,853,506

 
$
8.76

 
6.50
 
$
730,143

Exercisable at June 30, 2015
 
4,510,114

 
$
7.16

 
6.06
 
$
487,705
Summary of RSU Activity
A summary of the RSU activity under the 2013 Plan during the six months ended June 30, 2015 is presented below:
 
 
Number of Shares Underlying Outstanding RSUs
 
Weighted-Average Grant-Date Fair Value per RSU
 
 
 
 
 
Non-Vested outstanding at December 31, 2014
 
2,818,661

 
$
77.77

RSUs granted
 
2,041,106

 
102.12

RSUs vested
 
(357,242
)
 
82.42

RSUs forfeited
 
(79,987
)
 
82.48

Non-Vested outstanding at June 30, 2015
 
4,422,538

 
$
88.54
Summary of shares available for grant
The summary of shares available for issuance of equity based awards (including stock options and RSUs) during the six months ended June 30, 2015 is as follows:
 
 
Shares Available for Grant
Balance at December 31, 2014
 
6,229,892

Authorized
 
3,493,410

Granted
 
(2,041,106
)
Canceled
 
10

Forfeited
 
136,702

Balance at June 30, 2015
 
7,818,908