Noncontrolling and Redeemable Noncontrolling Interests - Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	$ (248)	$ 10,640	$ 6,259	$ 8,654
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	(608)	(47)	3,622	1,519	$ (3,005)
Income attributable to noncontrolling interests	(856)	10,593	(2,637)	10,173
Nonredeemable Noncontrolling Interest	21,434		21,434		445,174
Stagwell Global
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(248)	1,208	378	2,804
Income attributable to noncontrolling interests		1,161	(4,000)	4,323
Nonredeemable Noncontrolling Interest	21,434		21,434		21,746
Stagwell Media
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	0	9,432	(6,637)	5,850
Income attributable to noncontrolling interests		$ 9,432	6,637	$ 5,850
Nonredeemable Noncontrolling Interest	$ 0		$ 0		$ 423,428