Liability Related to Sale of Future Royalties - Schedule of Activity Within Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended
	Oct. 01, 2017	Jun. 30, 2018	Jun. 30, 2018
Liability Related To Sale Of Future Royalties [Line Items]
Non-cash royalty revenue payable to HCRP			$ (5,326)
Royalty Purchase Agreement
Liability Related To Sale Of Future Royalties [Line Items]
Liability related to sale of future royalties - beginning balance		$ 34,395	35,788
Deferred transaction costs recognized	$ (2,200)	198	401
Non-cash royalty revenue payable to HCRP		(2,544)	(5,326)
Non-cash interest expense recognized		1,134	2,320
Liability related to sale of future royalties - ending balance		$ 33,183	$ 33,183