Income Taxes - Effective Income Tax Rate Reconciliation (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Effective income tax rate reconciliation
U.S. Federal statutory tax rate	(35.00%)	(35.00%)	(35.00%)
Deferred state taxes, net of federal benefit	(3.10%)	(3.10%)	(1.20%)
Common stock warrant liability	(2.60%)	(2.30%)	20.60%
Other, net	(1.60%)	0.30%	0.70%
Foreign provision to return adjustment	(2.90%)
Change in unrecognized tax benefits	(0.70%)		(0.90%)
Change in valuation allowance	45.20%	40.10%	15.40%
Total effective income tax rate	(0.70%)	0.00%	(0.40%)