Income Taxes - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Line Items]
Income tax benefit	$ 0	$ 0	$ 6,631,000
Current income tax expense or benefit	0	0	0
Deferred income tax expense or benefit	0	0	(6,631,000)
Increase (decrease) in valuation allowance, deferred tax assets	64,200,000	82,500,000
Deferred capitalized start up expense net of amortization	300,000	400,000
Deferred income tax amortization	1,700,000	1,600,000
Research and development tax credit carryforwards	$ 5,034,000	4,620,000
Term of change in ownership of stockholders	3 years
Decrease in deferred tax assets	$ 44,900,000
Accrual for interest and penalties related to uncertain tax positions	$ 0	0	$ 0
Minimum
Income Tax Disclosure [Line Items]
Percentage of change in ownership of stockholders	50.00%
Percentage of change in ownership of stockholders holding outstanding stock	5.00%
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	$ 1,223,300,000	1,128,300,000
Net operating loss carryforwards indefinitely due to tax cut and jobs act	641,400,000
Research and development tax credit carryforwards	2,500,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	1,792,100,000	$ 1,620,700,000
Research and development tax credit carryforwards	$ 3,200,000
Keryx Biopharmaceuticals, Inc.
Income Tax Disclosure [Line Items]
Income tax benefit				$ 28,300,000