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Acquisitions and Dispositions - Narrative (Details) $ / shares in Units, £ in Thousands, shares in Thousands | Oct. 03, 2022 USD ($) | Jul. 15, 2022 USD ($) | Jul. 12, 2022 USD ($) | May 31, 2022 USD ($) | Apr. 19, 2022 USD ($) | Apr. 01, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2021 GBP (£) | Dec. 01, 2021 USD ($) | Oct. 01, 2021 USD ($) | Aug. 02, 2021 USD ($) $ / shares shares | Jul. 31, 2023 | Sep. 30, 2022 USD ($) | Dec. 31, 2021 GBP (£)
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Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  | $ 1,652,723,000 |  |  |  |  |  | $ 1,615,694,000 |
Payments for Acquire Businesses, Working Capital Payments | £ |  |  |  |  |  |  |  | £ 9 |  |  |  |  |  |
Stagwell Media |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash |  |  |  |  |  |  |  |  |  |  | $ 1.80 |  |  |
MDC |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable |  |  |  |  |  |  |  |  |  |  | $ 80,000,000 |  |  |
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life |  |  |  |  |  |  |  |  |  |  | 13 years |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | $ 1,290,347,000 |  |  |
Business Acquisition, Share Price | $ / shares |  |  |  |  |  |  |  |  |  |  | $ 5.42 |  |  |
MDC | Previously Reported Goodwill |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | $ 1,298,370,000 |  |  |
MDC | Common Class C | Stagwell Media |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, Acquisitions | shares |  |  |  |  |  |  |  |  |  |  | 179,970 |  |  |
MDC | Common Units | Stagwell OpCo |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining ownership interest acquired (percent) |  |  |  |  |  |  |  |  |  |  | 69.55% |  |  |
MDC | Integrated Agencies Network |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | $ 932,582,000 |  |  |
MDC | Media Network |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | 285,396,000 |  |  |
MDC | Communications Network |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | 72,369,000 |  |  |
Goodstuff Holdings Limited |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Closing cash payment | £ |  |  |  |  |  |  |  | 21 |  |  |  |  |  |
Goodwill |  |  |  |  |  |  | $ 4,410,000 |  |  |  |  |  |  |
Payment for contingent consideration | £ |  |  |  |  |  |  |  | 8 |  |  |  |  |  |
Payments to Acquire Businesses, Deferred Payments | £ |  |  |  |  |  |  |  | 4 |  |  |  |  |  |
Payment for contingent consideration | £ |  |  |  |  |  |  |  | 8 |  |  |  |  |  |
Payments to Acquire Businesses, Deferred Payments | £ |  |  |  |  |  |  |  | £ 4 |  |  |  |  |  |
Goodstuff Holdings Limited | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Deferred acquisition consideration | £ |  |  |  |  |  |  |  |  |  |  |  |  |  | £ 22
Targeted Victory |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining ownership interest acquired (percent) |  |  |  |  |  |  |  |  |  | 27.00% |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  |  | $ 73,898,000 |  |  |  |
Deferred acquisition consideration |  |  |  |  |  |  |  |  |  | $ 46,618,000 |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired, Step One |  |  |  |  |  |  |  |  |  | 13.30% |  |  |  |
Business Combination, Consideration Transferred, Redeemable Noncontrolling Interest |  |  |  |  |  |  |  |  |  | $ 27,280,000 |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired, Step One |  |  |  |  |  |  |  |  |  | 13.30% |  |  |  |
Business Combination, Consideration Transferred, Redeemable Noncontrolling Interest |  |  |  |  |  |  |  |  |  | $ 27,280,000 |  |  |  |
Targeted Victory | Forecast |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisitions, Percentage of Voting Interests Acquired, Step Two |  |  |  |  |  |  |  |  |  |  |  | 13.30% |  |
Business Acquisitions, Percentage of Voting Interests Acquired, Step Two |  |  |  |  |  |  |  |  |  |  |  | 13.30% |  |
Targeted Victory | Common Class A |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Contingent Consideration Arrangements, Purchase Price Option Sacrificed in Shares, Percentage |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High |  |  |  |  |  |  |  |  |  | $ 135,000 |  |  |  |
Business Combination, Contingent Consideration Arrangements, Purchase Price Option Sacrificed in Shares, Percentage |  |  |  |  |  |  |  |  |  | 50.00% |  |  |  |
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High |  |  |  |  |  |  |  |  |  | $ 135,000 |  |  |  |
Concentric |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining ownership interest acquired (percent) |  |  |  |  |  |  |  |  | 27.00% |  |  |  |  |
Aggregate purchase price |  |  |  |  |  |  |  |  | $ 8,058,000 |  |  |  |  |
Closing cash payment |  |  |  |  |  |  |  |  | 1,581,000 |  |  |  |  |
Deferred acquisition consideration |  |  |  |  |  |  |  |  | $ 6,477,000 |  |  |  |  |
Instrument Holdings Inc. |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining ownership interest acquired (percent) |  |  |  |  |  |  | 49.00% |  |  |  |  |  |  | 49.00%
Aggregate purchase price |  |  |  |  |  |  | $ 157,072,000 |  |  |  |  |  |  |
Closing cash payment |  |  |  |  |  |  | 37,500,000 |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Deferred Acquisition Payment |  |  |  |  |  |  | 82,072,000 |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Deferred Acquisition Payment |  |  |  |  |  |  | 82,072,000 |  |  |  |  |  |  |
Instrument Holdings Inc. | Common Class A |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable |  |  |  |  |  |  | $ 37,500,000 |  |  |  |  |  |  |
Hello Design |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  |  | $ 4,600,000 |  |  |  |  |  |  |  |
Closing cash payment |  |  |  |  |  | 3,600,000 |  |  |  |  |  |  |  |
Deferred acquisition consideration |  |  |  |  |  | $ 1,000,000 |  |  |  |  |  |  |  |
BNG |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  |  | $ 20,695,000 |  |  |  |  |  |  |  |  |
Goodwill |  |  |  |  |  |  |  |  |  |  | $ 25,552,000 |  |  |
Estimated contingent consideration |  |  |  |  | $ 50,000,000 |  |  |  |  |  |  |  |  |
Contingent consideration payable in cash (percent) |  |  |  |  | 67.00% |  |  |  |  |  |  |  |  |
Contingent consideration payable in equity (percent) |  |  |  |  | 33.00% |  |  |  |  |  |  |  |  |
TMA Direct |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Remaining ownership interest acquired (percent) |  |  |  | 87.00% |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  |  | $ 17,247,000 |  |  |  |  |  |  |  |  |  |
Deferred acquisition consideration |  |  |  | 457,000 |  |  |  |  |  |  |  |  |  |
Goodwill |  |  |  | $ 6,569,000 |  |  |  |  |  |  |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired, Step One |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High |  |  |  | $ 13,330,000 |  |  |  |  |  |  |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired, Step One |  |  |  | 13.00% |  |  |  |  |  |  |  |  |  |
Business Combination, Contingent Consideration Arrangements, Change in Range of Outcomes, Contingent Consideration, Liability, Value, High |  |  |  | $ 13,330,000 |  |  |  |  |  |  |  |  |  |
Epicenter | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price | $ 9,729,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Estimated contingent consideration | $ 5,000,000 |  |  |  |  |  |  |  |  |  |  |  |  |
PEP Group |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  |  | $ 521,000 |  |  |  |  |  |  |  |  |  |  |
Estimated contingent consideration |  |  | $ 2,679,000 |  |  |  |  |  |  |  |  |  |  |
Apollo |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business Acquisition [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate purchase price |  | $ 2,300,000 |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Business, First Payment |  | 1,000 |  |  |  |  |  |  |  |  |  |  |  |
Payments to Acquire Business, Second Payment |  | $ 1,500,000 |  |  |  |  |  |  |  |  |  |  |  |

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