Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Option Activity
A summary of the option activity during the six months ended June 30, 2017 follows:    
 
 
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, 2016
 
4,486,416

 
$
9.59

 
 
 
 
Options exercised
 
(1,018,437
)
 
7.88

 
 
 
 
Options canceled
 
(78
)
 
9.30

 
 
 
 
Options forfeited
 
(1,761
)
 
26.38

 
 
 
 
Balances at June 30, 2017
 
3,466,140

 
$
10.09

 
4.89
 
$
177,403

Vested and expected to vest at June 30, 2017
 
3,466,140

 
$
10.09

 
4.89
 
$
177,403

Exercisable at June 30, 2017
 
3,390,360

 
$
9.09

 
4.79
 
$
176,917
Summary of RSU Activity
A summary of the RSU activity during the six months ended June 30, 2017 follows:
 
 
Number of Shares Underlying Outstanding RSUs
 
Weighted-Average Grant-Date Fair Value per RSU
Non-Vested outstanding at December 31, 2016
 
7,141,294

 
$
65.62

RSUs granted
 
2,847,408

 
55.80

RSUs vested
 
(1,679,510
)
 
63.12

RSUs forfeited
 
(575,842
)
 
66.68

Non-Vested outstanding at June 30, 2017
 
7,733,350

 
$
62.62
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, 2017 follows:
 
 
Shares Available for Grant
 
 
2013 Plan
 
2013 ESPP
Balances at December 31, 2016
 
6,342,962

 
3,503,385

Authorized
 
3,835,921

 
767,184

Granted
 
(2,847,408
)
 
(362,606
)
Canceled
 
78

 
—

Forfeited
 
577,603

 
—

Balances at June 30, 2017
 
7,909,156

 
3,907,963