Research and Development Collaborative Arrangements - General Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2018	Jan. 01, 2018	Aug. 31, 2017
Research and development collaborative arrangements
Unbilled receivable			$ 12,702	$ 16,307
Collaborative arrangement | Celgene Switzerland LLC
Research and development collaborative arrangements
Unbilled receivable					$ 263,000
Upfront license fees received	$ 170,950	$ 92,050
Period of payment made (in years)			12 years
Upfront license fee receivable, allocated to acquisition					$ 13,000