Convertible Notes - Narrative (Details)	1 Months Ended	3 Months Ended		9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Debt Instrument [Line Items]
Convertible promissory notes, net of debt discount of $18,003 and $18,003, respectively (see Note 6)		$ 0		$ 0		$ 0
Accrued interest payable		2,334,000		2,334,000		1,738,000
Debt discount		18,003,000		$ 18,003,000		18,003,000
Expected term				5 years
Impact of 5% change in probability of change of control event in 2019				$ 300,000
Impact of 5% change in probability of change of control event in 2020				200,000
Impact of 5% change in the estimated credit spread				200,000
Derivative revaluation income (expense)		(3,522,000)	$ 87,000	(4,605,000)	$ 266,000
Warrants Issued With September 2016 Convertible Notes
Debt Instrument [Line Items]
Debt discount		9,598,000		9,598,000		9,598,000
Compounded Bifurcated Derivatives
Debt Instrument [Line Items]
Debt discount		1,267,000		1,267,000		$ 1,267,000
Beneficial Conversion Feature
Debt Instrument [Line Items]
Debt discount		$ 7,200,000		$ 7,200,000
Compounded Bifurcated Derivatives | Binomial Lattice Model | Dividend yield
Debt Instrument [Line Items]
Derivative liability, measurement input		0		0		0
Warrants Issued With September 2016 Convertible Notes
Debt Instrument [Line Items]
Warrants issued to purchase common stock (in shares) | shares	1,205,840
Convertible Debt
Debt Instrument [Line Items]
Convertible promissory notes, net of debt discount of $18,003 and $18,003, respectively (see Note 6)	$ 18,087,500	$ 18,000,000		$ 18,000,000
Interest rate	4.00%
Accrued interest payable		2,300,000		2,300,000
Additional amount over closing bid price (in usd per share) | $ / shares	$ 0.12625
Period after product candidate FCX-007 is approved to reach maturity	180 days
Required written notice period prior to exercise of put right	180 days
Prepayment as a percent of outstanding principal	101.00%
Principal value notes and related accrued interest converted to common stock		0		0
Debt discount		$ 18,100,000		18,100,000
Amortization of debt discount				$ 0	$ 0
Effective yield		1157.00%		1157.00%
Convertible Debt | Minimum
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares	$ 17.04375
Convertible Debt | Maximum
Debt Instrument [Line Items]
Conversion price (in dollars per share) | $ / shares	$ 18.39375