CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Product revenue, net	$ 20,074	$ 0	$ 20,074	$ 0
Costs and Expenses:
Costs of goods sold	1,669	0	1,669	0
Research and development	42,561	52,923	104,989	111,095
Sales and marketing	12,883	6,346	20,950	14,227
General and administrative	15,973	7,899	27,446	21,494
Total costs and expenses	73,086	67,168	155,054	146,816
Operating loss	(53,012)	(67,168)	(134,980)	(146,816)
Interest expense	(14,232)	(10,625)	(27,770)	(20,584)
Interest and other income	747	1,840	3,174	4,043
Loss before income tax	(66,497)	(75,953)	(159,576)	(163,357)
Income tax expense	0	0	0	0
Net loss	(66,497)	(75,953)	(159,576)	(163,357)
Net loss attributable to noncontrolling interest	(31)	0	(63)	(67)
Net loss attributable to Immunomedics, Inc. stockholders	$ (66,466)	$ (75,953)	$ (159,513)	$ (163,290)
Loss per common share attributable to Immunomedics, Inc. stockholders (basic and diluted) (in usd per share)	$ (0.30)	$ (0.40)	$ (0.73)	$ (0.85)
Weighted average shares used to calculated loss per common share (basic and diluted) (in shares)	225,306	191,745	219,210	191,401
Other comprehensive loss, net of tax:
Foreign currency translation adjustments	$ 7	$ 195	$ (2)	$ 186
Unrealized loss on securities available for sale	0	0	(225)	(200)
Other comprehensive gain (loss), net of tax:	7	195	(227)	(14)
Comprehensive loss	(66,490)	(75,758)	(159,803)	(163,371)
Comprehensive loss attributable to noncontrolling interest	(31)	0	(63)	(67)
Comprehensive loss attributable to Immunomedics, Inc. stockholders	$ (66,459)	$ (75,758)	$ (159,740)	$ (163,304)
Revenue, Product and Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember