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Employee benefit plans (Tables)
12 Months Ended
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Schedule of Share-based Compensation, Stock Options, Activity
A summary of the Company’s stock option activity in 2015 and related information is as follows:
 
Options outstanding
(shares in thousands)
Shares
 
Weighted- average
exercise price
 
Weighted-
average
remaining
contractual
term
(in years)
 
Aggregate
intrinsic value
(in thousands)
Outstanding at December 31, 2014:
25,134

 
$
6.62

 
7.09
 
$
1,425,339

Granted
792

 
39.66

 
 
 
 
Exercised
(12,375
)
 
2.01

 
 
 
 
Forfeited/Cancelled
(470
)
 
38.84

 
 
 
 
Outstanding at December 31, 2015:
13,081

 
$
11.82

 
6.70
 
$
108,846

 
 
 
 
 
 
 
 
Exercisable at December 31, 2015
8,449

 
$
6.19

 
5.89
 
$
103,696

Vested and expected to vest at December 31, 2015
12,858

 
$
11.62

 
6.67
 
$
108,681

Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block]
A summary of the Company's RSA activity in 2015 is as follows:
 
Shares
(in thousands)
 
Weighted-
average grant date fair value
 
Aggregate
intrinsic value
(in thousands)
Non-vested shares at December 31, 2014
17

 
$
6.30

 
$
1,017

Vested
(17)

 
 
 
 
Non-vested shares at December 31, 2015

 
 
 
 
Schedule of Share-based Compensation, Restricted Stock Units Award Activity
A summary of the Company’s RSU activity in 2015 and 2014 is as follows:
(shares in thousands)
Shares
 
Weighted- average grant date fair value
Non-vested shares at December 31, 2013
270

 
$
1.52

Granted
5,573

 
22.01

Vested
(1,533
)
 
18.42

Forfeited
(3
)
 
57.73

Non-vested shares at December 31, 2014
4,307

 
$
21.98

Granted
2,170

 
44.00

Vested
(1,735
)
 
19.84

Forfeited
(104
)
 
63.47

Non-vested shares at December 31, 2015
4,638

 
$
32.15

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
The fair value of stock options granted was estimated as of the grant date using the following assumptions:
 
Year ended December 31,
 
2015
 
2014
 
2013
Volatility
   43%–54%
 
   54%–56%
 
   56%–60%
Expected term (years)
5.5–7.0
 
5.3–6.3
 
5.3–6.1
Risk-free interest rate
1.6%–2.0%
 
1.7%–2.0%
 
0.8%–2.4%
Dividend yield
—%
 
—%
 
—%
Schedule of Share-based Payment Award, Equity Instruments Other Than Options, Valuation Assumptions [Table Text Block]
The fair value of stock purchase rights granted under the ESPP was estimated using the following assumptions:
 
Year ended December 31,
 
2015
 
2014
Volatility
   39%–45%
 
45.5%
Expected term (years)
0.5
 
0.6
Risk-free interest rate
   0.1%–0.2%
 
0.1%
Dividend yield
—%
 
—%
Allocation of Stock-based Compensation Expense
The following table summarizes stock-based compensation included in the consolidated statements of operations:
 
Year ended December 31,
(in thousands)
2015
 
2014
 
2013
Cost of revenue
$
1,492

 
$
835

 
$
690

Research and development
18,024

 
11,640

 
3,003
Sales and marketing
13,762

 
10,428

 
5,670
General and administrative
47,402

 
48,496

 
1,524
Total stock-based compensation expense, before income taxes
80,680

 
71,399

 
10,887

Total tax benefit recognized
(27,971
)
 
(19,471
)
 
(1,104
)
Total stock-based compensation expense, net of income taxes
$
52,709

 
$
51,928

 
$
9,783