Fair value (Details) - Fair value measurements on a recurring basis - USD ($) $ in Thousands |
Jun. 30, 2016 |
Dec. 31, 2015 |
---|---|---|
Assets: | ||
Total assets | $ 147,653 | $ 126,662 |
Level 1 | ||
Assets: | ||
Total assets | 95,894 | 43,224 |
Level 2 | ||
Assets: | ||
Total assets | 51,759 | 83,438 |
Cash and money market funds | ||
Assets: | ||
Total assets | 95,894 | 43,224 |
Cash and money market funds | Level 1 | ||
Assets: | ||
Total assets | 95,894 | 43,224 |
Corporate debt securities (including commercial paper) | ||
Assets: | ||
Total assets | 51,759 | 83,438 |
Corporate debt securities (including commercial paper) | Level 2 | ||
Assets: | ||
Total assets | $ 51,759 | $ 83,438 |