|
Stock-based compensation (Tables)
|
12 Months Ended |
|
Dec. 31, 2014
|
| Stock-based compensation |
|
| Schedule of stock-based compensation expense as reflected in the Company's consolidated statements of operations and comprehensive loss |
Stock-based compensation expense as reflected in the Company's consolidated statements of operations and comprehensive loss was as follows (in thousands):
|
|
|
Year Ended December 31,
|
|
|
|
|
2012
|
|
2013
|
|
2014
|
|
|
Research and development
|
|
$
|
2,956
|
|
$
|
3,575
|
|
$
|
3,727
|
|
|
General and administrative
|
|
|
4,444
|
|
|
6,818
|
|
|
8,385
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Total stock-based compensation expense
|
|
$
|
7,400
|
|
$
|
10,393
|
|
$
|
12,112
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Summary of unvested restricted stock activity and related information |
|
|
|
Shares
|
|
Weighted-average
grant date
fair value
per share
|
|
|
Unvested at December 31, 2013
|
|
|
329,282
|
|
$
|
0.034
|
|
|
Vested
|
|
|
(321,287
|
)
|
$
|
0.028
|
|
|
|
|
|
|
|
|
|
|
|
Unvested at December 31, 2014
|
|
|
7,995
|
|
$
|
0.28
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Summary of restricted stock units (RSUs) |
|
|
|
Shares
|
|
Weighted-average
grant date
fair value
per share
|
|
|
Unvested at December 31, 2013
|
|
|
529,850
|
|
$
|
10.78
|
|
|
Vested
|
|
|
(210,873
|
)
|
$
|
10.52
|
|
|
Forfeited
|
|
|
(25,230
|
)
|
$
|
10.32
|
|
|
|
|
|
|
|
|
|
|
|
Unvested at December 31, 2014
|
|
|
293,747
|
|
$
|
10.54
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| Summary of stock option activity and related information |
|
|
|
Shares
|
|
Weighted-average
exercise price
per share
|
|
Weighted-average
remaining
contractual term
(years)
|
|
Aggregate
intrinsic value
(in thousands)
|
|
|
Outstanding at December 31, 2013
|
|
|
2,388,062
|
|
$
|
8.62
|
|
|
8.8
|
|
$
|
6,768
|
|
|
Granted
|
|
|
1,956,415
|
|
$
|
12.39
|
|
|
|
|
|
|
|
|
Exercised
|
|
|
(30,451
|
)
|
$
|
0.68
|
|
|
|
|
|
|
|
|
Forfeited
|
|
|
(107,586
|
)
|
$
|
10.47
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Outstanding at December 31, 2014
|
|
|
4,206,440
|
|
$
|
10.38
|
|
|
8.4
|
|
$
|
2,593
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Vested at December 31, 2014
|
|
|
1,728,322
|
|
$
|
8.88
|
|
|
7.8
|
|
$
|
2,067
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Vested and expected to vest at December 31, 2014(1)
|
|
|
3,955,095
|
|
$
|
10.35
|
|
|
8.4
|
|
$
|
2,567
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
(1)
|
This represents the number of vested options as of December 31, 2014, plus the number of unvested options expected to vest as of December 31, 2014, based on the unvested options at December 31, 2014, adjusted for the estimated forfeiture rate.
|
|
| Schedule of assumptions used to estimate fair value of each stock option on grant date |
|
|
|
Year Ended December 31,
|
|
|
|
|
2012
|
|
2013
|
|
2014
|
|
|
Risk-free interest rate
|
|
|
1.14
|
%
|
|
1.14
|
%
|
|
1.99
|
%
|
|
Volatility
|
|
|
76
|
%
|
|
75
|
%
|
|
81
|
%
|
|
Dividend yield
|
|
|
—
|
|
|
—
|
|
|
—
|
|
|
Expected term (years)
|
|
|
6.0
|
|
|
6.0
|
|
|
6.0
|
|
|