Warrants - Additional Information (Details) - $ / shares	Dec. 31, 2017	Sep. 26, 2016	Apr. 30, 2016
Class B Common Stock | Subordinated Loan And Security Agreement
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares	27,321
Common stock issued through cashless exercise of warrant		25,658
Class B Common Stock | Subordinated Loan And Security Agreement
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares			21,208
Exercise price of warrant			$ 14.31
Class B Common Stock | Warrant Holder One
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares		10,604
Warrants outstanding	10,604
Series A Convertible Preferred Stock | Subordinated Loan And Security Agreement
Class Of Warrant Or Right [Line Items]
Warrants issued to purchase shares	27,321
Exercise price of warrant	$ 1.37255