Fair value measurements (Details) - USD ($)
$ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
Dec. 31, 2012 |
| Total financial assets |
$ 109,575
|
$ 15,167
|
|
|
| Transfers from Level 1 to Level 2 |
0
|
0
|
|
|
| Transfers from Level 2 to Level 1 |
0
|
0
|
|
|
| Cash and Cash Equivalents, at Carrying Value |
73,238
|
107,027
|
$ 43,070
|
$ 21,801
|
| Recurring basis |
|
|
|
|
| Total financial assets |
109,575
|
15,167
|
|
|
| Recurring basis | Level 1 |
|
|
|
|
| Total financial assets |
44,004
|
$ 15,167
|
|
|
| Recurring basis | Level 2 |
|
|
|
|
| Total financial assets |
65,571
|
|
|
|
| Recurring basis | Level 2 | Carrying Amount |
|
|
|
|
| Debt |
7,040
|
|
|
|
| Recurring basis | Level 2 | Fair Value |
|
|
|
|
| Debt |
6,952
|
|
|
|
| Money market funds | Recurring basis |
|
|
|
|
| Total financial assets |
39,998
|
|
|
|
| Money market funds | Recurring basis | Level 1 |
|
|
|
|
| Total financial assets |
39,998
|
|
|
|
| U.S. treasury notes |
|
|
|
|
| Total financial assets |
4,006
|
|
|
|
| U.S. treasury notes | Recurring basis |
|
|
|
|
| Total financial assets |
4,006
|
|
|
|
| U.S. treasury notes | Recurring basis | Level 1 |
|
|
|
|
| Total financial assets |
4,006
|
|
|
|
| US government agency securities |
|
|
|
|
| Total financial assets |
65,571
|
|
|
|
| US government agency securities | Recurring basis |
|
|
|
|
| Total financial assets |
65,571
|
|
|
|
| US government agency securities | Recurring basis | Level 2 |
|
|
|
|
| Total financial assets |
$ 65,571
|
|
|
|