Quarterly Results of Operations - Summarized Unaudited Quarterly Financial Data (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Consolidated Statements of Comprehensive Loss Data:
Revenues	$ 387,000	$ 482,000	$ 597,000	$ 690,000	$ 642,000	$ 1,323,000	$ 384,000	$ 742,000	$ 2,155,996	$ 3,091,250	$ 3,233,247
Net loss attributable to Immunomedics, Inc. stockholders	$ (117,032,000)	$ (35,546,000)	$ (2,514,000)	$ (118,745,000)	$ (53,255,000)	$ (59,306,000)	$ (24,447,000)	$ (16,198,000)	$ (273,836,887)	$ (153,205,945)	$ (59,036,950)
Loss per common share attributable to Immunomedics, Inc. stockholders (basic and diluted) (in USD per share)	$ (0.68)	$ (0.21)	$ (0.02)	$ (0.97)	$ (0.48)	$ (0.56)	$ (0.25)	$ (0.18)	$ (1.78)	$ (1.47)	$ (0.62)
Weighted average shares used to calculate loss per common share (basic and diluted) (in shares)	171,124,000	166,054,000	154,487,000	122,550,000	109,891,000	107,840,000	104,657,000	95,884,000	153,474,943	104,535,577	94,770,172