| In millions, except per share items | Dec-31-14 | Dec-31-13 | Dec-31-12 | Dec-31-11 | Dec-31-10 |
| | 10-K | 10-K | 10-K | 10-K/A | S-1/A |
| Assets | | | | | |
| Current assets: | | | | | |
| Cash and cash equivalents | 29.2 | 111.5 | 79.3 | 34.6 | |
| Marketable securities | 70.4 | 55.5 | | | |
| Prepaid expenses and other current assets | 1.5 | 1.2 | 0.6 | 1.1 | |
| Total current assets | 101.2 | 173.3 | 87.6 | 44.3 | |
| Property and equipment, net | 1.8 | 0.1 | 0.3 | 0.7 | |
| Other assets | 0.4 | 0.0 | 0.0 | 0.0 | |
| Total assets | 103.4 | 173.4 | 96.2 | 45.1 | |
| |
| Liabilities and stockholders' equity | | | | | |
| Current liabilities: | | | | | |
| Accounts payable | 4.7 | 3.2 | 2.2 | 1.0 | |
| Accrued personnel costs | 4.9 | 3.1 | 2.2 | 1.5 | |
| Accrued costs for services | 4.9 | 3.2 | 4.9 | 3.5 | |
| Accrued interest | 2.9 | 0.4 | 0.0 | | |
| Notes payable, current portion | 5.5 | 5.5 | 1.2 | | |
| Other current liabilities | 0.6 | | | | |
| Total current liabilities | 20.6 | 17.6 | 16.2 | 16.4 | |
| Notes payable-net of current portion | 22.7 | 6.0 | 2.8 | | |
| Other liabilities | 0.7 | 0.0 | | | |
| Total liabilities | 44.0 | 23.6 | 27.3 | 18.5 | |
| |
| Commitments and contingencies | | | | | |
| Stockholders' equity: | | | | | |
| Additional paid in capital | 367.3 | 322.1 | 189.2 | 2.5 | |
| Accumulated other comprehensive (loss) income | -0.1 | 0.0 | | | |
| Accumulated deficit | -307.8 | -172.2 | -120.3 | -83.5 | |
| Total stockholders' equity | 59.4 | 149.8 | 68.9 | -81.0 | |
| Total liabilities and stockholders' equity | 103.4 | 173.4 | 96.2 | 45.1 | |