Income Taxes - Reconciliation of effective tax rate (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Reconciliation of the effective tax rate to the U.S. Federal statutory rate | |||
| Federal tax benefit at statutory rate | 34.00% | 34.00% | 34.00% |
| State tax, net of Federal benefit | 8.00% | 3.00% | 6.00% |
| Loss due to change in fair value of convertible preferred stock liability | (19.00%) | ||
| Foreign rate differential | (23.00%) | ||
| Change in valuation allowance | (19.00%) | (18.00%) | (40.00%) |
| Effective income tax rate | 0.00% | 0.00% | 0.00% |
| Increased in valuation allowance | $ 7.0 | $ 5.8 | |