Kolltan Acquisition - Allocations of Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Nov. 29, 2016
Kolltan Acquisition
Estimated development costs included in expected future net cash flows	$ 132,000
Goodwill expected to be deductible for income tax purposes			$ 0
Summary of fair values of assets acquired and liabilities assumed
Goodwill		$ 90,976
Kolltan
Summary of fair values of assets acquired and liabilities assumed
Cash and cash equivalents			8,160
Other current and long-term assets			799
Property and equipment, net			2,072
In-process research and development (IPR&D)			61,690
Goodwill			82,011
Deferred tax liabilities, net			(23,393)
Other assumed liabilities			(9,974)
Total			121,365
Kolltan | Anti-KIT Program
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			40,000
Kolltan | CDX-3379
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			3,500
Kolltan | TAM programs
Summary of fair values of assets acquired and liabilities assumed
In-process research and development (IPR&D)			$ 18,000