Intangible Assets and Asset Acquisition Obligations - Remaining minimum royalty payments (Details) $ in Thousands	Mar. 31, 2018 USD ($)
Intangible Assets and Asset Acquisition Obligations
2018	$ 118,955
2019	135,000
2020	135,000
2021	135,000
Total remaining minimum royalty payments due	523,955
Less: Unamortized discount	(49,172)
Carrying value of minimum royalty payments	$ 474,783