|
Stock-based compensation (Details) (USD $)
|
12 Months Ended |
|
Dec. 31, 2014
item
|
Dec. 31, 2013
|
Dec. 31, 2012
|
| Stock-based compensation |
|
|
|
| Total stock-based compensation expense |
$ 12,112,000 |
$ 10,393,000 |
$ 7,400,000 |
| Liability classified stock-based compensation awards |
469,000 |
717,000 |
|
| Number of equity compensation plans |
2 |
|
|
| Vesting percentage in one year from vesting start date |
25.00% |
|
|
| Vesting period for twenty five percent from grant date |
1 year |
|
|
| Vesting percentage in equal quarterly installment |
6.25% |
|
|
| Vesting period for six and a quarter vesting percentage |
3 months |
|
|
| Expiration term |
10 years |
|
|
| Research and development |
|
|
|
| Stock-based compensation |
|
|
|
| Total stock-based compensation expense |
3,727,000 |
3,575,000 |
2,956,000 |
| General and administrative |
|
|
|
| Stock-based compensation |
|
|
|
| Total stock-based compensation expense |
$ 8,385,000 |
$ 6,818,000 |
$ 4,444,000 |