Asset Acquisitions and Contingent Consideration - Schedule of IPR&D Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development	$ 1,000	$ 20,898
GB001
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development		19,148
Other Programs
Acquired Finite Lived Intangible Assets [Line Items]
Total in process research and development	$ 1,000	$ 1,750