Common and Preferred Stock - Convertible Notes and Series D Financing (Details) - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Sep. 30, 2018	Sep. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Common and Preferred Stock
Proceeds from sale of preferred stock			$ 25,106,896
Common stock, par value (in dollars per share)				$ 0.001	$ 0.001
Convertible Notes
Common and Preferred Stock
Debt issued						$ 27,400,000
Interest rate (as a percent)						8.00%
Preferred stock - Series D
Common and Preferred Stock
Proceeds from sale of preferred stock	$ 25,600,000
Share price (in dollars per share)	$ 0.59808
Issuance of preferred stock (in shares)	91,147,482	91,147,482
Preferred stock - Series D | Convertible Notes
Common and Preferred Stock
Conversion of convertible debt	$ 28,900,000
Preferred stock - Series C-1
Common and Preferred Stock
Preferred stock, par value (in dollars per share)	$ 0.001