Emflaza asset acquisition - Narrative (Details) - USD ($) $ in Thousands		12 Months Ended
Apr. 20, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Issuance of common stock related to acquisition		$ 75,191
Intellectual Property
Finite-Lived Intangible Assets [Line Items]
Accumulated amortization		$ 15,400
Intellectual Property \| Marathon Pharmaceuticals, LLC
Finite-Lived Intangible Assets [Line Items]
Cash consideration	$ 75,000
Issuance of common stock related to acquisition (in shares)		6,683,598
Issuance of common stock related to acquisition	75,190
Acquisition costs	$ 2,163
Useful life	7 years
Non-collaborative Arrangement Transactions [Member] \| Marathon Pharmaceuticals, LLC
Finite-Lived Intangible Assets [Line Items]
Cash consideration	$ 75,000
Development and regulatory milestone payments which the entity may be obligated to pay	$ 50,000

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-Name Accounting Standards Codification
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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
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