Income Taxes - Tax Credit Carryforwards (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Orphan drug tax credit carryforwards
Tax Credit Carryforward
Tax credit carryforward	$ 162,653
Federal \| Research and development
Tax Credit Carryforward
Tax credit carryforward	150,598
State \| Research and development
Tax Credit Carryforward
Tax credit carryforward	$ 23,986

The amount of the tax credit carryforward, before tax effects, available to reduce future taxable income under enacted tax laws.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32559-109319

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant