Noncontrolling and Redeemable Noncontrolling Interests - Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Jun. 30, 2024	Dec. 31, 2024
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	$ 6,635	$ (224)
Net Income (Loss) Attributable to Redeemable Noncontrolling Interest	4,227	793	$ (3,005)
Income attributable to noncontrolling interests	(2,408)	569
Nonredeemable Noncontrolling Interest	445,493			$ 445,174
Stagwell Global
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	2	823
Income attributable to noncontrolling interests	(4,229)	(1,616)
Nonredeemable Noncontrolling Interest	21,497			21,746
Stagwell Media
Noncontrolling Interest [Line Items]
Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest	(6,637)	(1,047)
Income attributable to noncontrolling interests	6,637	$ 1,047
Nonredeemable Noncontrolling Interest	$ 423,996			$ 423,428