Accrued Expenses and Other Liabilities - Schedule of Accrued Expenses and Other Liabilities (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued compensation and benefits	$ 2,407,845	$ 1,435,015
Accrued professional fees	484,358	1,119,959
Accrued research and development expenses	825,494	182,500
Accrued unvested common stock subject to repurchase	130,063	122,551
Accrued expenses and other liabilities	$ 3,847,760	$ 2,860,025