Income Taxes - Reconciliation (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of the U.S. statutory income tax rate to the Company's effective tax rate
Federal income tax (benefit) at statutory rate (as a percent)	(34.00%)	(34.00%)	(34.00%)
Change in tax rate (as a percent)	29.60%	0.10%	0.30%
Permanent items (as a percent)	0.10%	0.90%	1.30%
Other (as a percent)	(0.90%)	0.20%	(0.00%)
Amended Tax Returns	(4.50%)	(0.00%)	(0.00%)
Change in valuation allowance (as a percent)	9.70%	32.80%	32.40%
Effective income tax rate (as a percent)	0.00%	0.00%	0.00%
Unrecognized tax benefits related to interest and penalties accrued	$ 0