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Stock-based compensation (Tables)
 3 Months Ended
Mar. 31, 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 three months ended March 31, 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
(28,463
)
 
5.66

 
 
 
 

Forfeited
(72,505
)
 
6.45

 
 
 
 

Canceled
(30,032
)
 
4.60

 
 
 
 
Balance as of March 31, 2018
3,051,544

 
$
12.35

 
8.1 years
 
$
22,479

 
 
 
 
 
 
 
 
Exercisable, March 31, 2018
1,326,527

 
$
6.89

 
6.9 years
 
$
16,797

The following table summarizes the activity for options that vest based upon the satisfaction of performance or market conditions for the three months ended March 31, 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
(23,460
)
 
2.16

 
 
 
 
Forfeited
(9,000
)
 
26.84

 
 
 
 
Canceled
(13,250
)
 
3.51

 
 
 
 
Balance as of March 31, 2018
2,360,827

 
$
6.56

 
7.2 years
 
$
33,334
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 three months ended March 31, 2018:
 
Shares of restricted stock outstanding
 
Weighted-average grant date fair value
Balance as of December 31, 2017
1,248,824

 
$
23.37

Granted
1,012,990

 
18.43

Vested
(172,065
)
 
26.80

Forfeited
(29,320
)
 
22.76

Balance as of March 31, 2018
2,060,429

 
$
20.66