Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Valuation allowance against net deferred tax assets (as a percentage)	100.00%	100.00%
Valuation allowance increase (decrease)	$ 51,800,000
Liability recorded for potential interest or penalties	0
Expected change to unrecognized tax benefit	0
State authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	144,200,000
Tax credit carryforward	9,800,000
Federal authority
Operating Loss Carryforwards [Line Items]
Net operating loss carryforward	221,500,000
Federal authority | Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	14,500,000
Federal authority | Orphan Drug Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	$ 1,700,000