Liability Related to Sale of Future Royalties - Schedule of Activity Within Liability Account from Inception of Royalty Agreement (Details) - USD ($) $ in Thousands		1 Months Ended	12 Months Ended
	Oct. 01, 2017	Dec. 31, 2017	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue payable to HCRP			$ (2,705)
Royalty Purchase Agreement
Liability Related to Sale of Future Royalties [Line Items]
Proceeds from sale of future royalties	$ 40,000	$ 40,000
Deferred transaction costs	$ (2,200)	(2,115)
Non-cash royalty revenue payable to HCRP		(2,705)	(2,700)
Non-cash interest expense recognized		608	600
Liability related to sale of future royalties - ending balance		$ 35,788	$ 35,788