Income Taxes - Reconciliation of Statutory U.S. Federal Rate to Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
U.S. federal taxes at statutory rate	(35.00%)	(34.00%)	(34.00%)
U.S. tax credits	(43.80%)	(3.40%)	(1.00%)
Warrants		23.00%	2.10%
Add back of Orphan Drug Credit	7.40%
Incentive stock option compensation	3.80%	1.80%	0.80%
Other	(0.60%)		0.20%
Foreign income tax rate differential	2.40%	0.40%
Change in valuation allowance	96.60%	11.90%	31.90%
Total	30.80%	(0.30%)