Income Taxes - Other (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2017
Provision for income taxes
Provision for income taxes			$ 0	$ 0	$ 0
Corporate tax rate			34.00%	34.00%	34.00%
Provisional reduction in Gross deferred tax assets	$ 50,400,000
Additional net income tax expense from the tax law change	0
Deferred tax assets
Deferred tax assets, before valuation allowance	99,848,000		$ 99,848,000	$ 75,265,000	$ 50,600,000
Valuation allowance	99,848,000		99,848,000	75,265,000
Forecast
Provision for income taxes
Corporate tax rate		21.00%
2016-09 Accounting Standards Update
Deferred tax assets
Deferred tax assets, before valuation allowance						$ 4,500,000
Valuation allowance						$ 4,500,000
Federal
Deferred tax assets
Net operating loss carryforwards	347,400,000		347,400,000	196,400,000	137,400,000
State
Deferred tax assets
Net operating loss carryforwards	$ 327,800,000		$ 327,800,000	$ 18,100,000	$ 15,400,000