Consolidated Statements of Stockholders’ Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	Total Stockholders’ Equity (Deficit) attributable to Millendo Therapeutics, Inc.	Total Equity Attributable to Noncontrolling Interests
Balance at beginning (in shares) at Dec. 31, 2018		13,357,999
Balance at beginning at Dec. 31, 2018	$ 73,122	$ 13	$ 234,876	$ (164,086)	$ 148	$ 70,951	$ 2,171
Stockholder's equity
Exercise of stock options (in shares)		97,225
Exercise of stock options	360		360			360
Exercise/forfeiture of BSPCE warrants (in shares)		17,713
Exercise/forfeiture of BSPCE warrants	111		527			527	(416)
Stock-based compensation expense	3,130		3,130			3,130
Foreign currency translation adjustment	(25)				(25)	(25)
Net loss	(31,869)			(31,869)		(31,869)
Balance at end (in shares) at Sep. 30, 2019		13,472,937
Balance at end at Sep. 30, 2019	44,829	$ 13	238,893	(195,955)	123	43,074	1,755
Balance at beginning (in shares) at Jun. 30, 2019		13,412,058
Balance at beginning at Jun. 30, 2019	55,025	$ 13	237,136	(184,323)	140	52,966	2,059
Stockholder's equity
Exercise of stock options (in shares)		51,278
Exercise of stock options	194		194			194
Exercise/forfeiture of BSPCE warrants (in shares)		9,601
Exercise/forfeiture of BSPCE warrants	63		367			367	(304)
Stock-based compensation expense	1,196		1,196			1,196
Foreign currency translation adjustment	(17)				(17)	(17)
Net loss	(11,632)			(11,632)		(11,632)
Balance at end (in shares) at Sep. 30, 2019		13,472,937
Balance at end at Sep. 30, 2019	44,829	$ 13	238,893	(195,955)	123	43,074	1,755
Balance at beginning (in shares) at Dec. 31, 2019		18,266,545
Balance at beginning at Dec. 31, 2019	59,871	$ 18	267,018	(208,654)	165	58,547	1,324
Stockholder's equity
Issuance of common stock, net of issuance costs (in shares)		719,400
Issuance of common stock, net of issuance costs	$ 5,650	$ 1	5,649			5,650
Exercise of stock options (in shares)	1,449	1,449
Exercise of stock options	$ 2		2			2
Exercise/forfeiture of BSPCE warrants (in shares)		12,307
Exercise/forfeiture of BSPCE warrants	78		734			734	(656)
Stock-based compensation expense	3,148		3,148			3,148
Foreign currency translation adjustment	109				109	109
Net loss	(29,044)			(29,044)		(29,044)
Balance at end (in shares) at Sep. 30, 2020		18,999,701
Balance at end at Sep. 30, 2020	39,814	$ 19	276,551	(237,698)	274	39,146	668
Balance at beginning (in shares) at Jun. 30, 2020		18,999,701
Balance at beginning at Jun. 30, 2020	$ 44,944	$ 19	275,463	(231,324)	118	44,276	668
Stockholder's equity
Exercise of stock options (in shares)	0
Stock-based compensation expense	$ 1,088		1,088			1,088
Foreign currency translation adjustment	156				156	156
Net loss	(6,374)			(6,374)		(6,374)
Balance at end (in shares) at Sep. 30, 2020		18,999,701
Balance at end at Sep. 30, 2020	$ 39,814	$ 19	$ 276,551	$ (237,698)	$ 274	$ 39,146	$ 668