Intangible Assets, Net - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Finite Lived Intangible Assets [Line Items]
Less accumulated amortization	$ (4,794)	$ (3,348)
Total intangible assets, net	87,468	88,914
Acquired and In-licensed Rights [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 2,262	2,262
Acquired and In-licensed Rights [Member] | Minimum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life	7 years
Acquired and In-licensed Rights [Member] | Maximum [Member]
Finite Lived Intangible Assets [Line Items]
Estimated useful life	21 years
Capitalized Regulatory Approval Milestones [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets, gross	$ 90,000	$ 90,000
Estimated useful life	16 years