Noncontrolling and Redeemable Noncontrolling Interests - Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		9 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Sep. 30, 2024	Dec. 31, 2024
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	$ 624	$ (1,762)	$ 6,011	$ (1,986)
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	3	773	4,230	1,566	$ (3,005)
Income attributable to noncontrolling interests	627	(989)	(1,781)	(420)
Nonredeemable Noncontrolling Interest	21,802		21,802			$ 445,174
Stagwell Global
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	624	773	626	1,596
Income attributable to noncontrolling interests		1,546	(4,856)	3,162
Nonredeemable Noncontrolling Interest	21,802		21,802			21,746
Stagwell Media
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	0	(2,535)	(6,637)	(3,582)
Income attributable to noncontrolling interests		$ (2,535)	6,637	$ (3,582)
Nonredeemable Noncontrolling Interest	$ 0		$ 0			$ 423,428