| Cover - USD ($) $ in Millions | 12 Months Ended | ||
| Dec. 31, 2020 | Mar. 31, 2021 | Jun. 30, 2020 | |
| Entity Information [Line Items] | |||
| Document Type | 10-K/A | ||
| Amendment Flag | false | ||
| Document Annual Report | true | ||
| Document Transition Report | false | ||
| Document Period End Date | Dec. 31, 2020 | ||
| Document Fiscal Period Focus | FY | ||
| Document Fiscal Year Focus | 2020 | ||
| Current Fiscal Year End Date | --12-31 | ||
| Entity File Number | 001-13718 | ||
| Entity Registrant Name | MDC PARTNERS INC. | ||
| Entity Central Index Key | 0000876883 | ||
| Entity Tax Identification Number | 98-0364441 | ||
| Entity Incorporation, State or Country Code | Z4 | ||
| Entity Address, Address Line One | One World Trade Center | ||
| Entity Address, Address Line Two | Floor 65 | ||
| Entity Address, City or Town | New York | ||
| Entity Address, State or Province | NY | ||
| Entity Address, Postal Zip Code | 10007 | ||
| City Area Code | 646 | ||
| Local Phone Number | 429-1800 | ||
| Title of 12(b) Security | Class A Subordinate Voting Shares, no par value | ||
| Trading Symbol | MDCA | ||
| Security Exchange Name | NASDAQ | ||
| Entity Well-known Seasoned Issuer | No | ||
| Entity Voluntary Filers | No | ||
| Entity Current Reporting Status | Yes | ||
| Entity Interactive Data Current | Yes | ||
| Entity Filer Category | Accelerated Filer | ||
| Entity Small Business | true | ||
| Entity Emerging Growth Company | false | ||
| Entity Shell Company | false | ||
| Entity Public Float | $ 120 | ||
| ICFR Auditor Attestation Flag | true | ||
| Common Class A [Member] | |||
| Entity Information [Line Items] | |||
| Entity Common Stock, Shares Outstanding | 74,787,317 | ||
| Common Class B [Member] | |||
| Entity Information [Line Items] | |||
| Entity Common Stock, Shares Outstanding | 3,743 |
