KOLLTAN ACQUISITION - Allocations of Assets and Liabilities (Details) - USD ($) $ in Thousands		12 Months Ended
	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2015
Summary of fair values of assets acquired and liabilities assumed at acquisition date
Goodwill		$ 90,976	$ 8,965
Kolltan
KOLLTAN ACQUISITION
Goodwill expected to be deductible for income tax purposes	$ 0
Summary of fair values of assets acquired and liabilities assumed at acquisition date
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
Maximum period for adjustments to purchase price allocation from acquisition date (in years)	1 year
Kolltan | CDX-0158
Summary of fair values of assets acquired and liabilities assumed at acquisition date
In-process research and development (IPR&D)	$ 40,000
Kolltan | CDX-3379
Summary of fair values of assets acquired and liabilities assumed at acquisition date
In-process research and development (IPR&D)	3,500
Kolltan | TAM programs
Summary of fair values of assets acquired and liabilities assumed at acquisition date
In-process research and development (IPR&D)	$ 18,000
Kolltan | CDX- 0158 CDX-3379 and TAM
Summary of fair values of assets acquired and liabilities assumed at acquisition date
Estimated development costs included in expected future net cash flows		$ 132,000