Warrants -Summary of Outstanding Warrants (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2016	May 11, 2015	Jan. 15, 2015	Aug. 22, 2014
Convertible Note Warrants
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	144,772
Exercise Price/Share	$ 14.00			$ 0.2189
Expiration Date	2022
Common Stock Warrants one
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	931
Exercise Price/Share	$ 6.45	$ 2.759
Expiration Date	2019
Common Stock Warrants
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	45,307
Exercise Price/Share	$ 2.76
Expiration Date	2026
Common Stock Tranche one
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	18,123
Exercise Price/Share	$ 7.73
Expiration Date	2028
Series E Redeemable Convertible Preferred Stock
Class Of Warrant Or Right [Line Items]
Shares of Common Stock Underlying Warrants	28,713
Exercise Price/Share	$ 23.51	$ 23.51	$ 23.51		$ 0.2189
Expiration Date	2024