Income Taxes - Summary of Reconciliation of Income Tax Expense (Benefit) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax benefit at statutory rate	$ (5,008,000)	$ (3,484,000)
State income tax, net of federal benefit	(1,593,000)	(528,000)
Permanent items	3,000	4,000
Fair value adjustments	15,000	(164,000)
Non-deductible interest expense	706,000	905,000
Stock-based compensation	45,000	21,000
Orphan drug credit	(475,000)	(616,000)
Research and development credits	(274,000)	(218,000)
Uncertain tax positions	222,000	209,000
Tax Cuts and Jobs Act	(15,000)	10,978,000
Change in valuation allowance	6,426,000	(7,110,000)
Other	(52,000)	3,000
Income tax expense (benefit)	$ 0	$ 0