Stock-based compensation (Tables)
 9 Months Ended
Sep. 30, 2012
Stock-based compensation  
Summary of the Company's stock option activity and related information

A summary of the Company’s stock option activity and related information is as follows (in thousands, except share and per share data):

 

 

 

Shares

 

Weighted
average
price per
share

 

Weighted
average
remaining
contractual
term
(years)

 

Aggregate
intrinsic
value

 

Outstanding at December 31, 2011

 

617,633

 

0.04

 

9.80

 

$

2,162

 

Granted

 

308,275

 

4.84

 

 

 

 

 

Forfeited

 

(98,366

)

0.29

 

 

 

 

 

Outstanding at September 30, 2012

 

827,542

 

1.80

 

9.29

 

$

3,046

 

Exercisable at September 30, 2012

 

115,784

 

0.34

 

9.04

 

$

595

 

Vested and expected to vest at September 30, 2012

 

761,507

 

1.78

 

9.04

 

$

2,817

 
Summary of the Company's restricted stock activity and related information

 

Shares

 

Weighted-average
purchase price
per share

 

Outstanding at December 31, 2011

 

2,319,646

 

$

0.002

 

Granted

 

—

 

 

 

Vested

 

(509,990

)

$

0.002

 

Outstanding at September 30, 2012

 

1,809,656

 

$

0.002

 

 
Schedule of assumptions used to estimate fair value of each stock-based award on the grant date using the Black-Scholes option pricing model

 

Three Months
Ended
September 30,

 

Nine Months Ended
September 30,

 

 

 

2012

 

2012

 

 

 

(Unaudited)

 

(Unaudited)

 

Risk-free interest rate

 

0.9

%

0.8 – 1.2

%

Dividend yield

 

—

 

—

 

Volatility

 

86 – 87

%

79 – 87

%

Expected term (years)

 

6.0 – 6.1

 

5.1 – 6.1