KOLLTAN ACQUISITION - Acquisition Related Expenses, Including Severance and Pro Forma Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended
	Nov. 29, 2016	Dec. 31, 2016	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
KOLLTAN ACQUISITION
Revenues			$ 1,874	$ 2,220	$ 1,389	$ 1,303	$ 1,790	$ 1,026	$ 2,178	$ 486	$ 6,786	$ 5,480	$ 3,586
Kolltan
KOLLTAN ACQUISITION
Acquisition-related expenses	$ 3,768	$ 700									700
Severance expenses		3,100
Revenues		$ 0
Pro Forma Financial Information
Revenue											6,786	5,480
Net loss											$ (146,905)	$ (157,690)
Basic and Diluted Net Loss Per Common Share											$ (1.24)	$ (1.37)
Kolltan | General and administrative
KOLLTAN ACQUISITION
Severance expenses											$ 2,400
Kolltan | Research and development
KOLLTAN ACQUISITION
Severance expenses											$ 700