Liability Related to Sale of Future Royalties - Carrying Value and Related Activity (Details) - USD ($) $ in Thousands	3 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Non-cash interest expense recognized, net of transaction cost amortization	$ 6,134
Liability related to sale of future royalties, gross	112,181
Less: Unamortized transaction costs	(262)
Liability related to sale of future royalties, net	$ 111,919	$ 0

Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28555-108399

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