UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current Assets
Cash and cash equivalents	$ 115,489	$ 92,457
Accounts receivable, net	669,612	225,733
Expenditures billable to clients	37,101	11,063
Other current assets	78,884	36,433
Total Current Assets	901,086	365,686
Fixed assets, net	118,526	35,614
Right-of-use lease assets - operating leases	334,867	57,752
Goodwill	1,619,272	351,725
Other intangible assets, net	945,081	186,035
Other assets	24,789	17,043
Total Assets	3,943,621	1,013,855
Current Liabilities
Accounts payable	277,385	147,826
Accruals and other liabilities	371,289	90,557
Advance billings	286,790	66,418
Current portion of lease liabilities - operating leases	74,162	19,579
Current portion of deferred acquisition consideration	60,951	12,579
Total Current Liabilities	1,070,577	336,959
Long-term debt	1,265,747	198,024
Long-term portion of deferred acquisition consideration	14,754	5,268
Long-term lease liabilities - operating leases	328,048	52,606
Deferred tax liabilities, net	134,288	16,050
Other liabilities	59,190	5,801
Total Liabilities	2,872,604	614,708
Redeemable Noncontrolling Interests	29,787	604
Commitments, Contingencies and Guarantees (Note 11)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Convertible preferred shares, 123,849,000 and 0 authorized, issued and outstanding at September 30, 2021 and December 31, 2020, respectively	209,980	0
Members' capital	0	358,756
Paid-in capital	169,537	0
Accumulated deficit	(6,153)	0
Accumulated other comprehensive income	12,537	0
Stagwell Inc. Shareholders' Equity	385,980	358,756
Noncontrolling interests	655,250	39,787
Total Shareholders' Equity	1,041,230	398,543
Liabilities and Equity, Total	3,943,621	1,013,855
Common Class A and Common Class B
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common shares	77	0
Common Class C
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Common shares	$ 2	$ 0