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Stock-based compensation (Tables)
 9 Months Ended
Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of Stock Option Activity and Related Information
The following table summarizes the activity for options that vest solely based upon the satisfaction of a service condition for the nine months ended September 30, 2018:
 
Options
outstanding
 
Weighted-average exercise price
 
Weighted-average remaining
contractual life
(in years)
 
Aggregate intrinsic
values
(in thousands)
Balance as of December 31, 2017
2,597,294

 
$
10.66

 
 
 
 

Granted
585,250

 
18.43

 
 
 
 

Exercised
(147,210
)
 
3.19

 
 
 
 

Canceled or forfeited
(186,572
)
 
9.77

 
 
 
 

Balance as of September 30, 2018
2,848,762

 
$
12.70

 
7.7
 
$
9,647

 
 
 
 
 
 
 
 
Exercisable, September 30, 2018
1,479,548

 
$
9.06

 
6.9
 
$
8,172

The following table summarizes the activity for options that vest based upon the satisfaction of performance or market conditions for the nine months ended September 30, 2018:
 
Options
outstanding
 
Weighted-average exercise price
 
Weighted-average remaining
contractual life
(in years)
 
Aggregate intrinsic
values
(in thousands)
Balance as of December 31, 2017
2,406,537

 
$
6.58

 
 
 
 
Exercised
(309,105
)
 
3.32

 
 
 
 
Canceled or forfeited
(22,250
)
 
12.95

 
 
 
 
Balance as of September 30, 2018
2,075,182

 
$
6.99

 
6.6
 
$
17,748
Summary of Activities for Restricted Stock Awards ("RSAs") and Restricted Stock Units ("RSUs")
The following table summarizes the activities for restricted stock awards (“RSAs”) and restricted stock units (“RSUs”) for the nine months ended September 30, 2018:
 
Shares of restricted stock outstanding
 
Weighted-average grant date fair value
Balance as of December 31, 2017
1,248,824

 
$
23.37

Granted
1,277,485

 
17.96

Vested
(337,115
)
 
23.08

Canceled or forfeited
(163,685
)
 
20.27

Balance as of September 30, 2018
2,025,509

 
$
20.25