Stagwell (STGW) 10-Q 10 May 21 2021 Q1 Quarterly report Financial data

Cover Page

Cover Page - shares	3 Months Ended
	Mar. 31, 2021	Apr. 30, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	001-13718
Entity Registrant Name	MDC Partners Inc
Entity Incorporation, State or Country Code	Z4
Entity Tax Identification Number	98-0364441
Entity Address, Address Line One	One World Trade Center, 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 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 Central Index Key	0000876883
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Class A
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		77,181,293
Common Class B
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		3,743

UNAUDITED CONDENSED CONSOLIDATE

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenue:
Services	$ 307,585	$ 327,742
Operating expenses:
Cost of services sold	186,921	222,694
Office and general expenses	83,946	66,354
Depreciation and amortization	8,176	9,206
Impairment and other losses	875	161
Costs and Expenses, Total	279,918	298,415
Operating income	27,667	29,327
Other income (expense):
Interest expense and finance charges, net	(19,065)	(15,611)
Foreign exchange gain (loss)	2,080	(14,757)
Other, net	614	16,334
Nonoperating Income (Expense), Total	(16,371)	(14,034)
Income before income taxes and equity in earnings of non-consolidated affiliates	11,296	15,293
Income tax expense	1,302	13,500
Income before equity in earnings of non-consolidated affiliates	9,994	1,793
Equity in losses of non-consolidated affiliates	(493)	0
Net income	9,501	1,793
Net income attributable to the noncontrolling interest	(4,491)	(791)
Net income attributable to MDC Partners Inc.	5,010	1,002
Net income (loss) attributable to MDC Partners Inc. common shareholders	$ 921	$ (2,438)
Basic and diluted
Earnings per share, basic	$ 0.01	$ (0.03)
Earnings per share, diluted	$ 0.01	$ (0.03)
Weighted Average Number of Common Shares Outstanding:
Weighted Average Number of Shares Outstanding, Basic	73,392,824	72,397,661,000
Weighted Average Number of Shares Outstanding, Diluted	75,439,066	72,397,661,000
Series 4 Convertible Preferred Stock [Domain] | Preferred Stock
Other income (expense):
Accretion on and net income allocated to convertible preference shares	$ (4,089)	$ (3,440)

UNAUDITED CONSOLIDATED STATEMEN

UNAUDITED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Comprehensive income (loss)
Net loss	$ 9,501	$ 1,793
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	(3,507)	7,429
Other comprehensive income (loss)	(3,507)	7,429
Comprehensive income for the period	5,994	9,222
Comprehensive income attributable to the noncontrolling interests	(3,539)	(282)
Comprehensive income attributable to MDC Partners Inc.	$ 2,455	$ 8,940

UNAUDITED CONDENSED CONSOLIDA_2

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current Assets:
Cash and cash equivalents	$ 113,340	$ 60,757
Accounts receivable, less allowance for doubtful accounts of $4,498 and $5,473	377,670	374,892
Expenditures billable to clients	22,824	10,552
Other current assets	31,687	40,938
Total Current Assets	545,521	487,139
Fixed assets, at cost, less accumulated depreciation of $137,729 and $136,166	85,085	90,413
Right-of-use assets - operating leases	207,418	214,188
Goodwill	669,060	668,211
Other intangible assets, net	30,784	33,844
Other assets	22,845	17,517
Total Assets	1,560,713	1,511,312
Current Liabilities
Accounts payable	209,679	168,396
Accruals and other liabilities	242,667	274,968
Current portion of lease liabilities - operating leases	41,229	41,208
Current portion of deferred acquisition consideration	52,156	53,730
Total Current Liabilities	715,890	691,258
Long-term debt	864,850	843,184
Long-term portion of deferred acquisition consideration	41,244	29,335
Long-term lease liabilities - operating leases	241,375	247,243
Other liabilities	77,585	82,065
Total Liabilities	1,940,944	1,893,085
Redeemable Noncontrolling Interests	25,352	27,137
Commitments, Contingencies and Guarantees (Note 9)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract]
Convertible preference shares, 145,000 authorized, issued and outstanding at March 31, 2021 and December 31, 2020	152,746	152,746
Common stock and other paid-in capital	106,193	104,367
Accumulated deficit	(704,741)	(709,751)
Accumulated other comprehensive income	183	2,739
MDC Partners Inc. Shareholders' Deficit	(445,619)	(449,899)
Noncontrolling interests	40,036	40,989
Total Shareholders' Deficit	(405,583)	(408,910)
Liabilities and Equity, Total	$ 1,560,713	$ 1,511,312

UNAUDITED CONDENSED CONSOLIDA_3

UNAUDITED CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 4,498	$ 5,473
Fixed assets, accumulated depreciation	$ 137,729	$ 136,166
Preference shares, authorized (in shares)	145,000	145,000
Preference shares, issued (in shares)	145,000	145,000
Preference shares, outstanding (in shares)	145,000	145,000

UNAUDITED CONDENSED CONSOLIDA_4

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ 9,501	$ 1,793
Adjustments to reconcile net income to cash provided by (used in) operating activities:
Stock-based compensation	(1,963)	3,070
Depreciation and amortization	8,176	9,206
Impairment and other losses	875	161
Adjustment to deferred acquisition consideration	11,685	(4,600)
Deferred income taxes	63	8,511
Changes in working capital:
Accounts receivable	(2,779)	41,148
Expenditures billable to clients	(12,272)	7,370
Prepaid expenses and other current assets	(7,615)	(3,385)
Accounts payable, accruals and other liabilities	23,977	(62,120)
Acquisition related payments	(473)	(782)
Advance billings	17,203	(24,816)
Net cash provided by (used in) operating activities	47,060	(19,955)
Cash flows from investing activities:
Capital expenditures	(13,423)	(1,546)
Proceeds from sale of assets	7,080	18,920
Acquisitions, net of cash acquired	0	(729)
Other	(689)	0
Net cash provided by (used in) investing activities	(7,032)	16,645
Repayment of borrowing under revolving credit facility
Acquisition related payments	(1,087)	(750)
Distributions to noncontrolling interests and other	(5,486)	(4,608)
Net cash provided by financing activities	13,427	119,642
Effect of exchange rate changes on cash and cash equivalents	(872)	(2,164)
Net increase in cash and cash equivalents	52,583	114,168
Cash and cash equivalents at beginning of period	60,757	106,933
Cash and cash equivalents at end of period	113,340	221,101
Supplemental disclosures:
Cash income taxes paid	251	849
Cash interest paid	317	145
Wells Fargo Capital Finance, LLC | Revolving Credit Facility
Repayment of borrowing under revolving credit facility
Repayment of borrowing under revolving credit facility	(140,950)	(125,333)
Proceeds from revolving credit facility	$ 160,950	$ 250,333

UNAUDITED CONDENSED CONSOLIDA_5

UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	Convertible Preference Shares	Common Shares	Common Stock and Other Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	MDC Partners Inc. Shareholders' Deficit	Noncontrolling Interests	Series 4 Convertible Preferred Stock [Member]Convertible Preference Shares
Balance at Dec. 31, 2019	$ (190,575)	$ 152,746		$ 101,469	$ (480,779)	$ (4,269)	$ (230,833)	$ 40,258
Balance (in shares) at Dec. 31, 2019									145,000,000
Common stock, balance (in shares) at Dec. 31, 2019			72,154,603
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	1,002				1,002
Other comprehensive loss	7,429					7,938	7,938	(509)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			587,227
Shares acquired and cancelled	(637)			(637)			(637)
Shares acquired and cancelled (in shares)			(258,664)
Stock-based compensation	476			476			476
Changes in redemption value of redeemable noncontrolling interests	(1,218)			(1,218)			(1,218)
Business acquisitions and step-up transactions, net of tax	(503)			(503)			(503)
Other	82			0	82		82	0
Balance at Mar. 31, 2020	(183,944)	152,746		99,587	(479,695)	3,669	(223,693)	39,749
Balance (in shares) at Mar. 31, 2020									145,000,000
Common stock, balance (in shares) at Mar. 31, 2020			72,483,166
Balance at Dec. 31, 2020	(408,910)	152,746		104,367	(709,751)	2,739	(449,899)	40,989
Balance (in shares) at Dec. 31, 2020									145,000,000
Common stock, balance (in shares) at Dec. 31, 2020			73,532,848
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	5,010				5,010
Other comprehensive loss	(3,507)					(2,555)	(2,555)	(952)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			1,322,732
Shares acquired and cancelled	(202)			(202)			(202)
Shares acquired and cancelled (in shares)			(64,520)
Stock-based compensation	1,035			1,035			1,035
Changes in redemption value of redeemable noncontrolling interests	1,681			1,681			1,681
Business acquisitions and step-up transactions, net of tax	(330)			(330)			(330)
Other	(360)			(358)	0		(359)	(1)
Balance at Mar. 31, 2021	$ (405,583)	$ 152,746		$ 106,193	$ (704,741)	$ 183	$ (445,619)	$ 40,036
Balance (in shares) at Mar. 31, 2021									145,000,000
Common stock, balance (in shares) at Mar. 31, 2021			74,791,060

Basis of Presentation and Recen

Basis of Presentation and Recent Developments	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Recent Developments	Basis of Presentation and Recent Developments MDC Partners Inc. (the “Company” or “MDC”), incorporated under the laws of Canada, is a leading provider of global marketing, advertising, activation, communications and strategic consulting solutions. Through its Networks (and underlying agencies generally referred to as “Partner Firms”), MDC delivers a wide range of customized services in order to drive growth and business performance for its clients. The accompanying consolidated financial statements include the accounts of MDC, its subsidiaries and variable interest entities for which the Company is the primary beneficiary. MDC has prepared the unaudited condensed consolidated interim financial statements included herein in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for reporting interim financial information on Form 10-Q. Accordingly, the financial statements have been condensed and do not include certain information and disclosures pursuant to these rules. The preparation of financial statements in conformity with GAAP requires us to make judgments, assumptions and estimates about current and future results of operations and cash flows that affect the amounts reported and disclosed. Actual results could differ from these estimates and assumptions. The consolidated results for interim periods are not necessarily indicative of results for the full year and should be read in conjunction with the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 (“2020 10-K”). The COVID-19 pandemic continues to negatively affect the global economy and the Company’s operations. The pandemic did not begin to impact the Company’s operations in a significant manner until the second quarter of 2020. Therefore, our first quarter of 2021 comparisons to the first quarter of 2020 are affected by the impact of the pandemic on our operations in the first quarter of 2021. Early in 2020, the Company took actions to combat the impact of COVID-19 on our operations. We will continue to monitor the worldwide public health threat, government actions to combat COVID-19 and the impact such developments may have on the overall economy, our clients and operations. If the impact of the pandemic is beyond our expectation, the Company believes it is well positioned through the actions implemented at the beginning of the pandemic to successfully work through the effects of COVID-19 in 2021. The impact of the pandemic and the corresponding actions are reflected in our judgments, assumptions and estimates in the preparation of the financial statements. The judgments, assumptions and estimates will be updated and could result in different results in the future depending on the continued impact of the COVID-19 pandemic. The accompanying financial statements reflect all adjustments, consisting of normally recurring accruals, which in the opinion of management are necessary for a fair presentation, in all material respects, of the information contained therein. Intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications have been made to the prior year financial information to conform to the current year presentation. Recent Developments On December 21, 2020, MDC and Stagwell Media LP (“Stagwell”) announced that they had entered into a definitive transaction agreement (the “Transaction Agreement”) providing for the combination of MDC with the subsidiaries of Stagwell that own and operate a portfolio of marketing services companies (the “Stagwell Entities”). The combination and related transactions, including the domestication of MDC to a Delaware corporation, are referred to as the “Transactions.” See “Item 1. Business – Recent Developments” in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020, filed on March 16, 2021, for a description of the Transactions. On May 7, 2021, MDC’s proxy statement/prospectus on Form S-4, as filed on April 30, 2021, which describes the Transaction Agreement, the Transactions, and related ancillary agreements in more detail, was declared effective by the SEC. MDC’s Board of Directors has scheduled a special meeting of shareholders on June 22, 2021 for the Company’s shareholders to vote on proposals to approve the Transactions and related matters. On April 26, 2021, the Company acquired the remaining 40% ownership interest of Gale Partners it did not already own for an aggregate purchase price of approximately $20,000. The purchase price will be made in a combination of cash and MDC Class A Common Shares, of which approximately $12,000 is deferred with payments due in April 2022 and 2023. As part of the closing date purchase price, the Company issued 2,131,574 Class A Common Shares to the seller in a private placement in reliance on exemptions from registration under the Securities Act of 1933, as amended.

Acquisitions and Dispositions

Acquisitions and Dispositions	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions 2020 Acquisition On July 1, 2020, the Company acquired the remaining 10% ownership interest of Veritas it did not already own for an aggregate purchase price of $2,187, of which $1,087 was a deferred cash payment. As a result of the transaction, the Company reduced noncontrolling and redeemable noncontrolling interests by $2,651. The difference between the purchase price and the noncontrolling interest of $464 was recorded in Common stock and other paid-in capital in the Unaudited Condensed Consolidated Balance Sheets. On March 19, 2020, the Company acquired the remaining 22.5% ownership interest of KWT Global it did not already own for an aggregate purchase price of $2,118, comprised of a closing cash payment of $729 and contingent deferred acquisition payments with an estimated present value at the acquisition date of $1,389. The contingent deferred payments were based on the financial results of the underlying business from 2019 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $1,615. The difference between the purchase price and the redeemable noncontrolling interest of $503 was recorded in Common stock and other paid-in capital in the Unaudited Condensed Consolidated Balance Sheets. 2020 Disposition On February 14, 2020, the Company sold substantially all the assets and certain liabilities of Sloane and Company LLC (“Sloane”), an indirectly wholly owned subsidiary of the Company, to an affiliate of The Stagwell Group LLC (“Stagwell”), for an aggregate sale price of $26,696, consisting of cash received at closing plus contingent deferred payments expected to be paid over the next two years. The sale resulted in a gain of $16,827, which is included in Other, net within the Unaudited Condensed Consolidated Statements of Operations. Sloane was included within Allison & Partners which is included within the All Other category. Deferred acquisition consideration on the balance sheet consists of deferred obligations related to contingent and fixed purchase price payments, and to a lesser extent, contingent and fixed retention payments tied to continued employment of specific personnel. Contingent deferred acquisition consideration is recorded at the acquisition date fair value and adjusted at each reporting period through operating income, for contingent purchase price payments, or net interest expense, for fixed purchase price payments. The Company accounts for certain retention payments through operating income as stock-based compensation over the required retention period. The following table presents changes in contingent deferred acquisition consideration, which is measured at fair value on a recurring basis using significant unobservable inputs, and a reconciliation to the amounts reported on the balance sheets as of March 31, 2021 and December 31, 2020. March 31, December 31, 2021 2020 Beginning Balance of Contingent Payments $ 82,802 $ 74,671 Payments (1,153) (46,792) Redemption value adjustments (1) 12,392 44,993 Additions - Acquisitions and step-up transactions — 7,703 Other (641) 2,227 Ending balance of contingent payments $ 93,400 $ 82,802 Fixed Payments — 263 $ 93,400 $ 83,065 (1) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments and stock-based compensation charges relating to acquisition payments that are tied to continued employment. Redemption value adjustments are recorded within Office and general expenses on the Unaudited Condensed Consolidated Statements of Operations. The following table presents the impact to the Company’s Statements of operations due to the redemption value adjustments for the contingent deferred acquisition consideration: Three Months Ended March 31, 2021 2020 Loss (income) attributable to fair value adjustments $ 11,685 $ (4,600) Stock-based compensation 707 2,025 Redemption value adjustments $ 12,392 $ (2,575)

Revenue

Revenue	3 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue	Revenue The Company’s revenue recognition policies are established in accordance with ASC 606, and accordingly, revenue is recognized when control of the promised goods or services is transferred to our clients, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. The MDC network provides an extensive range of services to our clients, offering a variety of marketing and communication capabilities including strategy, creative and production for advertising campaigns across a variety of platforms (print, digital, social media, television broadcast), public relations services including strategy, editorial, crisis support or issues management, media training, influencer engagement and events management. We also provide media buying and planning across a range of platforms (out-of-home, paid search, social media, lead generation, programmatic, television broadcast), experiential marketing and application/website design and development. The primary source of the Company’s revenue is from agency arrangements in the form of fees for services performed, commissions, and from performance incentives or bonuses, depending on the terms of the client contract. In all circumstances, revenue is only recognized when collection is reasonably assured. Certain of the Company’s contractual arrangements have more than one performance obligation. For such arrangements, revenue is allocated to each performance obligation based on its relative stand-alone selling price. Stand-alone selling prices are determined based on the prices charged to clients or using expected cost plus margin. The determination of our performance obligations is specific to the services included within each contract. Based on a client’s requirements within the contract, and how these services are provided, multiple services could represent separate performance obligations or be combined and considered one performance obligation. Contracts that contain services that are not significantly integrated or interdependent, and that do not significantly modify or customize each other, are considered separate performance obligations. Typically, we consider media planning, media buying, creative (or strategy), production and experiential marketing services to be separate performance obligations if included in the same contract as each of these services can be provided on a stand-alone basis, and do not significantly modify or customize each other. Public relations services and application/website design and development are typically each considered one performance obligation as there is a significant integration of these services into a combined output. We typically satisfy our performance obligations over time, as services are performed. Fees for services are typically recognized using input methods (direct labor hours, materials and third-party costs) that correspond with efforts incurred to date in relation to total estimated efforts to complete the contract. Point in time recognition primarily relates to certain commission-based contracts, which are recognized upon the placement of advertisements in various media when the Company has no further performance obligation. Revenue is recognized net of sales and other taxes due to be collected and remitted to governmental authorities. The Company’s contracts typically provide for termination by either party within 30 to 90 days. Although payment terms vary by client, they are typically within 30 to 60 days. In addition, the Company generally has the right to payment for all services provided through the end of the contract or termination date. Within each contract, we identify whether the Company is principal or agent at the performance obligation level. In arrangements where the Company has substantive control over the service before transferring it to the client, and is primarily responsible for integrating the services into the final deliverables, we act as principal. In these arrangements, revenue is recorded at the gross amount billed. Accordingly, for these contracts the Company has included reimbursed expenses in revenue. In other arrangements where a third-party supplier, rather than the Company, is primarily responsible for the integration of services into the final deliverables, and thus the Company is solely arranging for the third-party supplier to provide these services to our client, we generally act as agent and record revenue equal to the net amount retained, when the fee or commission is earned. The role of MDC’s agencies under a production services agreement is to facilitate a client’s purchasing of production capabilities from a third-party production company in accordance with the client’s strategy and guidelines. The obligation of MDC’s agencies under media buying services is to negotiate and purchase advertising media from a third-party media vendor on behalf of a client to execute its media plan. We do not obtain control prior to transferring these services to our clients; therefore, we primarily act as agent for production and media buying services. A small portion of the Company’s contractual arrangements with clients include performance incentive provisions, which allow the Company to earn additional revenues as a result of its performance relative to both quantitative and qualitative goals. Incentive compensation is primarily estimated using the most likely amount method and is included in revenue up to the amount that is not expected to result in a reversal of a significant amount of cumulative revenue recognized. We recognize revenue related to performance incentives as we satisfy the performance obligation to which the performance incentives are related. Disaggregated Revenue Data The Company provides a broad range of services to a large base of clients across the full spectrum of industry verticals globally. The primary source of revenue is from agency arrangements in the form of fees for services performed, commissions, and from performance incentives or bonuses. Certain clients may engage with the Company in various geographic locations, across multiple disciplines, and through multiple Partner Firms. Representation of a client rarely means that MDC handles marketing communications for all brands or product lines of the client in every geographical location. The Company’s Partner Firms often cooperate with one another through referrals and the sharing of both services and expertise, which enables MDC to service clients’ varied marketing needs by crafting custom integrated solutions. Additionally, the Company maintains separate, independent operating companies to enable it to effectively manage potential conflicts of interest by representing competing clients across the MDC network. The following table presents revenue disaggregated by client industry vertical for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, Industry Reportable Segment 2021 2020 Food & Beverage All $ 55,178 $ 58,091 Retail All 30,777 36,303 Consumer Products All 45,405 39,769 Communications All 16,990 41,045 Automotive All 15,629 25,192 Technology All 46,390 25,535 Healthcare All 31,494 24,066 Financials All 24,442 24,005 Transportation and Travel/Lodging All 9,948 20,486 Other All 31,332 33,250 $ 307,585 $ 327,742 MDC has historically largely focused where the Company was founded in North America, the largest market for its services in the world. The Company has expanded its global footprint to support clients looking for help to grow their businesses in new markets. MDC’s Partner Firms are located in the United States, Canada, and an additional eleven countries around the world. In the past, some clients have responded to weakening economic conditions with reductions to their marketing budgets, which included discretionary components that are easier to reduce in the short term than other operating expenses. The following table presents revenue disaggregated by geography for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, Geographical Location Reportable Segment 2021 2020 United States All $242,580 $264,561 Canada All 22,650 18,256 Other All 42,355 44,925 $307,585 $327,742 Contract Assets and Liabilities Contract assets consist of fees and reimbursable outside vendor costs incurred on behalf of clients when providing advertising, marketing and corporate communications services that have not yet been invoiced to clients. Unbilled service fees were $59,143 and $49,110 at March 31, 2021 and December 31, 2020, respectively, and are included as a component of Accounts receivable on the Unaudited Condensed Consolidated Balance Sheets. Outside vendor costs incurred on behalf of clients which have yet to be invoiced were $22,824 and $10,552 at March 31, 2021 and December 31, 2020, respectively, and are included on the Unaudited Condensed Consolidated Balance Sheets as Expenditures billable to clients. Such amounts are invoiced to clients at various times over the course of providing services. Contract liabilities consist of fees billed to clients in excess of fees recognized as revenue and are classified as Advance billings and included within Accruals and other liabilities on the Company’s Unaudited Condensed Consolidated Balance Sheets. In arrangements in which we are acting as an agent, the revenue recognition related to the contract liability is presented on a net basis within the Unaudited Condensed Consolidated Statements of Operations. Advance billings at March 31, 2021 and December 31, 2020 were $170,159 and $152,956, respectively. The increase in the Advance billings balance of $17,203 for the three months ended March 31, 2021 was primarily driven by cash payments received or due in advance of satisfying our performance obligations, offset by $99,188 of revenues recognized that were included in the Advance billings balances as of December 31, 2020 and reductions due to the incurrence of third-party costs. Contract liabilities classified within Accruals and other liabilities at March 31, 2021 and December 31, 2020 were $97,075 and $112,755, respectively. The decrease in the balance of $15,680 for the three months ended March 31, 2021 was primarily driven by cash payments received or due in advance of satisfying our performance obligations, offset by $69,699 of revenues recognized that were included in the balance as of December 31, 2020 and reductions due to the incurrence of third-party costs. Changes in the contract asset and liability balances during the three months ended March 31, 2021 were not materially impacted by write offs, impairment losses or any other factors. The majority of our contracts are for periods of one year or less. For those contracts with a term of more than one year, we had approximately $5,799 of unsatisfied performance obligations as of March 31, 2021, of which we expect to recognize approximately 83% in 2021 and 17% in 2022.

Income (Loss) Per Common Share

Income (Loss) Per Common Share	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Loss Per Common Share	Income (Loss) Per Common Share The following table sets forth the computation of basic and diluted income (loss) per common share: Three Months Ended March 31, 2021 2020 Numerator: Net income attributable to MDC Partners Inc. $ 5,010 $ 1,002 Accretion on convertible preference shares (3,724) (3,440) Net income allocated to convertible preference shares (365) — Net income (loss) attributable to MDC Partners Inc. common shareholders $ 921 $ (2,438) Adjustment to net income allocated to convertible preference shares 7 — Net income (loss) attributable to MDC Partners Inc. common shareholders - Diluted $ 928 $ (2,438) Denominator: Basic weighted average number of common shares outstanding 73,392,824 72,397,661 Diluted weighted average number of common shares outstanding 75,439,066 72,397,661 Basic $ 0.01 $ (0.03) Diluted $ 0.01 $ (0.03) Anti-dilutive stock awards 1,920,634 2,835,770

Deferred Acquisition Considerat

Deferred Acquisition Consideration	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Deferred Acquisition Consideration	Acquisitions and Dispositions 2020 Acquisition On July 1, 2020, the Company acquired the remaining 10% ownership interest of Veritas it did not already own for an aggregate purchase price of $2,187, of which $1,087 was a deferred cash payment. As a result of the transaction, the Company reduced noncontrolling and redeemable noncontrolling interests by $2,651. The difference between the purchase price and the noncontrolling interest of $464 was recorded in Common stock and other paid-in capital in the Unaudited Condensed Consolidated Balance Sheets. On March 19, 2020, the Company acquired the remaining 22.5% ownership interest of KWT Global it did not already own for an aggregate purchase price of $2,118, comprised of a closing cash payment of $729 and contingent deferred acquisition payments with an estimated present value at the acquisition date of $1,389. The contingent deferred payments were based on the financial results of the underlying business from 2019 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $1,615. The difference between the purchase price and the redeemable noncontrolling interest of $503 was recorded in Common stock and other paid-in capital in the Unaudited Condensed Consolidated Balance Sheets. 2020 Disposition On February 14, 2020, the Company sold substantially all the assets and certain liabilities of Sloane and Company LLC (“Sloane”), an indirectly wholly owned subsidiary of the Company, to an affiliate of The Stagwell Group LLC (“Stagwell”), for an aggregate sale price of $26,696, consisting of cash received at closing plus contingent deferred payments expected to be paid over the next two years. The sale resulted in a gain of $16,827, which is included in Other, net within the Unaudited Condensed Consolidated Statements of Operations. Sloane was included within Allison & Partners which is included within the All Other category. Deferred acquisition consideration on the balance sheet consists of deferred obligations related to contingent and fixed purchase price payments, and to a lesser extent, contingent and fixed retention payments tied to continued employment of specific personnel. Contingent deferred acquisition consideration is recorded at the acquisition date fair value and adjusted at each reporting period through operating income, for contingent purchase price payments, or net interest expense, for fixed purchase price payments. The Company accounts for certain retention payments through operating income as stock-based compensation over the required retention period. The following table presents changes in contingent deferred acquisition consideration, which is measured at fair value on a recurring basis using significant unobservable inputs, and a reconciliation to the amounts reported on the balance sheets as of March 31, 2021 and December 31, 2020. March 31, December 31, 2021 2020 Beginning Balance of Contingent Payments $ 82,802 $ 74,671 Payments (1,153) (46,792) Redemption value adjustments (1) 12,392 44,993 Additions - Acquisitions and step-up transactions — 7,703 Other (641) 2,227 Ending balance of contingent payments $ 93,400 $ 82,802 Fixed Payments — 263 $ 93,400 $ 83,065 (1) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments and stock-based compensation charges relating to acquisition payments that are tied to continued employment. Redemption value adjustments are recorded within Office and general expenses on the Unaudited Condensed Consolidated Statements of Operations. The following table presents the impact to the Company’s Statements of operations due to the redemption value adjustments for the contingent deferred acquisition consideration: Three Months Ended March 31, 2021 2020 Loss (income) attributable to fair value adjustments $ 11,685 $ (4,600) Stock-based compensation 707 2,025 Redemption value adjustments $ 12,392 $ (2,575)

Leases

Leases	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Leases	Leases The Company leases office space in North America, Europe, Asia, South America, and Australia. This space is primarily used for office and administrative purposes by the Company’s employees in performing professional services. These leases are classified as operating leases and expire between years 2021 through 2033. The Company’s finance leases are immaterial. The Company’s leasing policies are established in accordance with ASC 842, and accordingly, the Company recognizes on the balance sheet at the time of lease commencement a right-of-use lease asset and a lease liability, initially measured at the present value of the lease payments. Right-of-use lease assets represent the Company’s right to use an underlying asset for the lease term and lease liabilities represent the Company’s obligation to make lease payments arising from the lease. All right-of-use lease assets are reviewed for impairment. As the Company’s implicit rate in its leases is not readily determinable, in determining the present value of lease payments, the Company uses its incremental borrowing rate based on the information available at the commencement date. Lease payments included in the measurement of the lease liability are comprised of noncancelable lease payments, payments based upon an index or rate, payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and payments for early termination options unless it is reasonably certain the lease will not be terminated early. Lease costs are recognized in the Unaudited Condensed Consolidated Statements of Operations over the lease term on a straight-line basis. Leasehold improvements are depreciated on a straight-line basis over the lesser of the term of the related lease or the estimated useful life of the asset. Some of the Company’s leases contain variable lease payments, including payments based upon an index or rate. Variable lease payments based upon an index or rate are initially measured using the index or rate in effect at the lease commencement date and are included within the lease liabilities. Lease liabilities are not remeasured as a result of changes in the index or rate, rather changes in these types of payments are recognized in the period in which the obligation for those payments is incurred. In addition, some of our leases contain variable payments for utilities, insurance, real estate tax, repairs and maintenance, and other variable operating expenses. Such amounts are not included in the measurement of the lease liability and are recognized in the period when the facts and circumstances which the variable lease payments are based upon occur. Some of the Company’s leases include options to extend or renew the leases through 2040. The renewal and extension options are not included in the lease term as the Company is not reasonably certain that it will exercise its option. From time to time, the Company enters into sublease arrangements both with unrelated third-parties and with our partner agencies. These leases are classified as operating leases and expire between years 2021 through 2027. Sublease income is recognized over the lease term on a straight-line basis. Currently, the Company subleases office space in North America, Asia, Europe and Australia. As of March 31, 2021, the Company has entered into five operating leases for which the commencement date has not yet occurred as the premises are in the process of being prepared for occupancy by the landlord. Accordingly, these five leases represent an obligation of the Company that is not reflected within the Unaudited Condensed Consolidated Balance Sheets as of March 31, 2021. The aggregate future liability related to these leases is approximately $34,020. The discount rate used for leases accounted for under ASC 842 is the Company’s collateralized credit adjusted borrowing rate. The following table presents lease costs and other quantitative information for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 Lease Cost: Operating lease cost $ 17,127 $ 16,391 Variable lease cost 2,593 4,655 Sublease rental income (2,564) (2,805) Total lease cost $ 17,156 $ 18,241 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 16,796 $ 17,635 Right-of-use lease assets obtained in exchange for operating lease liabilities and other non-cash adjustments $ 3,816 $ 7,119 Weighted average remaining lease term (in years) - Operating leases 7.2 7.0 Weighted average discount rate - Operating leases 10.6 8.7 In the three months ended March 31, 2021, the Company recorded a charge of $875 to reduce the carrying value of two of its right-of-use lease assets and accelerate the operating expenses of one of its right-of-use lease assets. These right-of-use lease assets related to three agencies within its Integrated Networks - Group B reportable segment. The Company evaluated the facts and circumstances related to the use of the assets which indicated that they may not be recoverable. Using adjusted quoted market prices to develop expected future cash flows, it was determined that the fair value of the assets were less than their carrying value. This impairment charge is included in Impairment and other losses within the Unaudited Condensed Consolidated Statements of Operations. In the three months ended March 31, 2020, the Company recorded an impairment charge of $161 to reduce the carrying value of one of its right-of-use lease assets. Operating lease expense is included in office and general expenses in the Unaudited Condensed Consolidated Statements of Operations. The Company’s lease expense for leases with a term of 12 months or less is immaterial. The following table presents minimum future rental payments under the Company’s leases at March 31, 2021 and their reconciliation to the corresponding lease liabilities: Maturity Analysis Remaining 2021 $52,871 2022 61,447 2023 56,839 2024 50,615 2025 39,582 2026 and thereafter 152,702 Total 414,056 Less: Present value discount (131,452) Lease liability $ 282,604

Debt

Debt	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Debt	Debt As of March 31, 2021 and December 31, 2020, the Company’s indebtedness was comprised as follows: March 31, 2021 December 31, 2020 Revolving Credit Agreements $ 20,000 $ — Senior Notes 870,256 870,256 Debt Issuance Cost (25,406) (27,072) $ 864,850 $ 843,184 Senior Notes On March 23, 2016, MDC entered into an indenture (the “Indenture”) among MDC, its existing and future restricted subsidiaries that guarantee, are co-borrowers under, or grant liens to secure, the Credit Agreement (as defined below), as guarantors (the “Guarantors”) and The Bank of New York Mellon, as trustee, relating to the issuance by MDC of $900,000 aggregate principal amount of the senior notes due 2024 (the “Senior Notes”). The Senior Notes were sold in a private placement in reliance on exemptions from registration under the Securities Act of 1933. The Senior Notes bear interest, payable semiannually in arrears on May 1 and November 1, at a rate of 7.50% per annum. The Senior Notes mature on May 1, 2024, unless earlier redeemed or repurchased. The Senior Notes are guaranteed on a senior unsecured basis by all of MDC’s existing and future restricted subsidiaries that guarantee, are co-borrowers under, or grant liens to secure, the Credit Agreement. The Senior Notes are unsecured and unsubordinated obligations of MDC and rank (i) equally in right of payment with all of MDC’s or any Guarantor’s existing and future senior indebtedness, (ii) senior in right of payment to MDC’s or any Guarantor’s existing and future subordinated indebtedness, (iii) effectively subordinated to all of MDC’s or any Guarantor’s existing and future secured indebtedness to the extent of the collateral securing such indebtedness, including the Credit Agreement, and (iv) structurally subordinated to all existing and future liabilities of MDC’s subsidiaries that are not Guarantors. MDC may, at its option, redeem the Senior Notes in whole at any time or in part from time to time, at varying prices based on the timing of the redemption. If MDC experiences certain kinds of changes of control (as defined in the Indenture), holders of the Senior Notes may require MDC to repurchase any Senior Notes held by them at a price equal to 101% of the principal amount of the Senior Notes plus accrued and unpaid interest. In addition, if MDC sells assets under certain circumstances, it must apply the proceeds from such sale and offer to repurchase the Senior Notes at a price equal to 100% of the principal amount plus accrued and unpaid interest. The Indenture includes covenants that, among other things, restrict MDC’s ability and the ability of its restricted subsidiaries (as defined in the Indenture) to incur or guarantee additional indebtedness; pay dividends on or redeem or repurchase the capital stock of MDC; make certain types of investments; create restrictions on the payment of dividends or other amounts from MDC’s restricted subsidiaries; sell assets; enter into transactions with affiliates; create liens; enter into sale and leaseback transactions; and consolidate or merge with or into, or sell substantially all of MDC’s assets to, another person. These covenants are subject to a number of important limitations and exceptions. The Senior Notes are also subject to customary events of default, including a cross-payment default and cross-acceleration provision. The Company was in compliance with all covenants at March 31, 2021. Revolving Credit Agreement The Company is party to a $211,500 secured revolving credit facility due February 3, 2022. The Company had $20,000 outstanding under the revolving credit facility as of March 31, 2021. Advances under the Credit Agreement bear interest as follows: (i) Non-Prime Rate Loans bear interest at the Non-Prime Rate plus the Non-Prime Rate Margin and (ii) all other Obligations bear interest at the Prime Rate, plus the Prime Rate Margin. The Non-Prime Rate Margin and Prime Rate Margin will range from 2.50% to 3.00% for Non-Prime Rate Loans and from 1.75% to 2.25% for Prime Rate Loans. In addition to paying interest on outstanding principal under the Credit Agreement, MDC is required to pay an unused revolver fee to lenders under the Credit Agreement in respect of unused commitments thereunder. The Credit Agreement, which includes financial and non-financial covenants, is guaranteed by substantially all of MDC’s present and future subsidiaries, other than immaterial subsidiaries and subject to customary exceptions, and collateralized by a portion of MDC’s outstanding receivable balance. The Company was in compliance with all of the terms and conditions of its Credit Agreement as of March 31, 2021. At March 31, 2021 and December 31, 2020, the Company had issued undrawn outstanding letters of credit of $19,151 and $18,651, respectively.

Noncontrolling and Redeemable N

Noncontrolling and Redeemable Noncontrolling Interests	3 Months Ended
	Mar. 31, 2021
Noncontrolling Interest [Abstract]
Noncontrolling and Redeemable Noncontrolling Interests	Noncontrolling and Redeemable Noncontrolling Interests When acquiring less than 100% ownership of an entity, the Company may enter into agreements that give the Company an option to purchase, or require the Company to purchase, the incremental ownership interests under certain circumstances. Where the option to purchase the incremental ownership is within the Company’s control, the amounts are recorded as noncontrolling interests in the equity section of the Company’s Unaudited Condensed Consolidated Balance Sheets. Where the incremental purchase may be required of the Company, the amounts are recorded as redeemable noncontrolling interests in mezzanine equity at their estimated acquisition date redemption value and adjusted at each reporting period for changes to their estimated redemption value through additional paid-in capital (but not less than their initial redemption value), except for foreign currency translation adjustments. On occasion, the Company may initiate a renegotiation to acquire an incremental ownership interest and the amount of consideration paid may differ materially from the amounts recorded in the Company’s Unaudited Condensed Consolidated Balance Sheets. Noncontrolling Interests Changes in amounts due to noncontrolling interest holders included in Accruals and other liabilities on the Unaudited Condensed Consolidated Balance Sheets for the year ended December 31, 2020 and three months ended March 31, 2021 were as follows: Noncontrolling Balance at December 31, 2019 $ 14,028 Income attributable to noncontrolling interests 21,774 Distributions made (15,192) Other 94 Balance at December 31, 2020 $ 20,704 Income attributable to noncontrolling interests 4,491 Distributions made (5,285) Other 36 Balance at March 31, 2021 $ 19,946 Changes in the Company’s ownership interests in our less than 100% owned subsidiaries during the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 Net income attributable to MDC Partners Inc. $ 5,010 $ 1,002 Transfers from the noncontrolling interest: Decrease in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests (330) (503) Net transfers from noncontrolling interests $ (330) $ (503) Change from Net income attributable to MDC Partners Inc. and transfers to noncontrolling interests $ 4,680 $ 499 Redeemable Noncontrolling Interests The following table presents changes in redeemable noncontrolling interests: Three Months Ended March 31, 2021 Year Ended December 31, 2020 Beginning Balance $ 27,137 $ 36,973 Redemptions — (12,289) Granted — — Changes in redemption value (1,681) 2,800 Currency translation adjustments (104) (347) Ending Balance $ 25,352 $ 27,137 The noncontrolling shareholders’ ability to exercise any such option right is subject to the satisfaction of certain conditions, including conditions requiring notice in advance of exercise and specific employment termination conditions. In addition, these rights cannot be exercised prior to specified staggered exercise dates. The exercise of these rights at their earliest contractual date would result in obligations of the Company to fund the related amounts during 2021 to 2025. It is not determinable, at this time, if or when the owners of these rights will exercise all or a portion of these rights. The redeemable noncontrolling interest of $25,352 as of March 31, 2021, consists of $16,469 assuming that the subsidiaries perform over the relevant future periods at their discounted cash flows earnings level and such rights are exercised, $8,883 upon termination of such owner’s employment with the applicable subsidiary or death and $0 representing the initial redemption value (required floor) recorded for certain acquisitions in excess of the amount the Company would have to pay should the Company acquire the remaining ownership interests for such subsidiaries.

Commitments, Contingencies and

Commitments, Contingencies and Guarantees	3 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Guarantees	Commitments, Contingencies, and Guarantees Legal Proceedings. The Company’s operating entities are involved in legal proceedings of various types. While any litigation contains an element of uncertainty, the Company has no reason to believe that the outcome of such proceedings or claims will have a material adverse effect on the financial condition or results of operations of the Company. Deferred Acquisition Consideration and Options to Purchase. See Notes 5 and 8 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for information regarding potential payments associated with deferred acquisition consideration and the acquisition of noncontrolling shareholders’ ownership interest in subsidiaries. Natural Disasters. Certain of the Company’s operations are located in regions of the United States which typically are subject to hurricanes. During the three months ended March 31, 2021 and 2020, these operations did not incur any material costs related to damages resulting from hurricanes. Guarantees . Generally, the Company has indemnified the purchasers of certain assets in the event that a third party asserts a claim against the purchaser that relates to a liability retained by the Company. These types of indemnification guarantees typically extend for a number of years. Historically, the Company has not made any significant indemnification payments under such agreements and no amount has been accrued in the accompanying consolidated financial statements with respect to these indemnification guarantees. The Company continues to monitor the conditions that are subject to guarantees and indemnifications to identify whether it is probable that a loss has occurred and would recognize any such losses under any guarantees or indemnifications in the period when those losses are probable and estimable. Commitments. At March 31, 2021, the Company had $19,151 of undrawn letters of credit. The Company entered into operating leases for which the commencement date has not yet occurred as of March 31, 2021. See Note 6 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for additional information.

Share Capital

Share Capital	3 Months Ended
	Mar. 31, 2021
Share Capital [Abstract]
Share Capital	Share Capital The authorized and outstanding share capital of the Company is as follows: Series 6 Convertible Preference Shares On March 14, 2019 (the “Series 6 Issue Date”), the Company entered into a securities purchase agreement with Stagwell Agency Holdings LLC (“Stagwell Holdings”), an affiliate of Stagwell, pursuant to which Stagwell Holdings agreed to purchase (i) 14,285,714 newly authorized Class A shares (the “Stagwell Class A Shares”) for an aggregate contractual purchase price of $50,000 and (ii) 50,000 newly authorized Series 6 convertible preference shares (“Series 6 Preference Shares”) for an aggregate contractual purchase price of $50,000. The Company received proceeds of approximately $98,620 net of fees and estimated expenses, which were primarily used to pay down existing debt under the Company’s credit facility and for general corporate purposes. The proceeds allocated to the Stagwell Class A Shares were $35,997 and to Series 6 Preference Shares were $62,623 based on their relative fair value calculated by utilizing a Monte Carlo Simulation model. In connection with the closing of the transaction, the Company increased the size of its Board and appointed two nominees designated by Stagwell Holdings. Except as required by law, the Series 6 Preference Shares do not have voting rights and are not redeemable at the option of Stagwell Holdings. The holders of the Series 6 Preference Shares have the right to convert their Series 6 Preference Shares in whole at any time and from time to time, and in part at any time and from time to time, into a number of Class A Shares equal to the then-applicable liquidation preference divided by the applicable conversion price at such time (the “Conversion Price”). The initial liquidation preference per share of each Series 6 Preference Share is $1,000. The initial Conversion Price is $5.00 per Series 6 Preference Share, subject to customary adjustments for share splits and combinations, dividends, recapitalizations and other matters, including weighted average anti-dilution protection for certain issuances of equity or equity-linked securities. The Series 6 Preference Shares’ liquidation preference accretes at 8.0% per annum, compounded quarterly until the five-year anniversary of the Series 6 Issue Date. During the three months ended March 31, 2021, the Series 6 Preference Shares accreted at a monthly rate of 7.69, for total accretion of $1,153, bringing the aggregate liquidation preference to $58,804 as of March 31, 2021. The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. See Note 4 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for further information regarding the Series 6 Preference Shares. Holders of the Series 6 Preference Shares are entitled to dividends in an amount equal to any dividends that would otherwise have been payable on the Class A Shares issued upon conversion of the Series 6 Preference Shares. The Series 6 Preference Shares are convertible at the Company’s option (i) on and after the two-year anniversary of the Series 6 Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least 125% of the Conversion Price or (ii) after the fifth anniversary of the Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least equal to the Conversion Price. Following certain change in control transactions of the Company in which holders of Series 6 Preference Shares are not entitled to receive cash or qualifying listed securities with a value at least equal to the liquidation preference plus accrued and unpaid dividends, (i) holders will be entitled to cash dividends on the liquidation preference at an increasing rate (beginning at 7%), and (ii) the Company will have a right to redeem the Series 6 Preference Shares for cash at the greater of their liquidation preference plus accrued and unpaid dividends or their as-converted value. Series 4 Convertible Preference Shares On March 7, 2017 (the “Series 4 Issue Date”), the Company issued 95,000 newly created Preference Shares (“Series 4 Preference Shares”) to affiliates of The Goldman Sachs Group, Inc. (collectively, the “Purchaser”) pursuant to a $95,000 private placement. The Company received proceeds of approximately $90,123, net of fees and estimated expenses, which were primarily used to pay down existing debt under the Company’s credit facility and for general corporate purposes. In connection with the closing of the transaction, the Company increased the size of its Board and appointed one nominee designated by the Purchaser. Except as required by law, the Series 4 Preference Shares do not have voting rights and are not redeemable at the option of the Purchaser. Subsequent to the ninetieth day following the Series 4 Issue Date, the holders of the Series 4 Preference Shares have the right to convert their Series 4 Preference Shares in whole at any time and from time to time and in part at any time and from time to time into a number of Class A Shares equal to the then-applicable liquidation preference divided by the applicable conversion price at such time (the “Conversion Price”). The initial liquidation preference per share of each Series 4 Preference Share is $1,000. The Conversion Price of a Series 4 Preference Share is subject to customary adjustments for share splits and combinations, dividends, recapitalizations and other matters, including weighted average anti-dilution protection for certain issuances of equity or equity-linked securities. In connection with the anti-dilution protection provision triggered by the issuance of equity securities to Stagwell Holdings, the Conversion Price per Series 4 Preference Share was reduced to $7.42 from the initial Conversion Price of $10.00. The Series 4 Preference Shares’ liquidation preference accretes at 8.0% per annum, compounded quarterly until the five-year anniversary of the Series 4 Issue Date. During the three months ended March 31, 2021, the Series 4 Preference Shares accreted at a monthly rate of approximately $9.02 per Series 4 Preference Share, for total accretion of $2,571, bringing the aggregate liquidation preference to $131,110 as of March 31, 2021. The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. See Note 4 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for further information regarding the Series 4 Preference Shares. Holders of the Series 4 Preference Shares are entitled to dividends in an amount equal to any dividends that would otherwise have been payable on the Class A Shares issued upon conversion of the Series 4 Preference Shares. The Series 4 Preference Shares are convertible at the Company’s option (i) on and after the two-year anniversary of the Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least 125% of the Conversion Price or (ii) after the fifth anniversary of the Series 4 Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least equal to the Conversion Price. Following certain change in control transactions of the Company in which holders of Series 4 Preference Shares are not entitled to receive cash or qualifying listed securities with a value at least equal to the liquidation preference plus accrued and unpaid dividends, (i) holders will be entitled to cash dividends on the liquidation preference at an increasing rate (beginning at 7%), and (ii) the Company will have a right to redeem the Series 4 Preference Shares for cash at the greater of their liquidation preference plus accrued and unpaid dividends or their as-converted value. Class A Common Shares (“Class A Shares”) These are an unlimited number of subordinate voting shares, carrying one vote each, with a par value of $0, entitled to dividends equal to or greater than Class B Shares, convertible at the option of the holder into one Class B Share for each Class A Share after the occurrence of certain events related to an offer to purchase all Class B shares. There were 74,787,317 and 73,529,105 Class A Shares issued and outstanding as of March 31, 2021 and December 31, 2020, respectively. Class B Common Shares (“Class B Shares”) These are an unlimited number of voting shares, carrying twenty votes each, with a par value of $0, convertible at any time at the option of the holder into one Class A share for each Class B share. There were 3,743 and 3,743 Class B Shares issued and outstanding as of March 31, 2021 and December 31, 2020, respectively.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements A fair value measurement assumes a transaction to sell an asset or transfer a liability occurs in the principal market for the asset or liability or, in the absence of a principal market, the most advantageous market for the asset or liability. In determining fair value, the Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible as well as considers counterparty credit risk in its assessment of fair value. The hierarchy for observable and unobservable inputs used to measure fair value into three broad levels are described below: • Level 1 - Quoted prices (unadjusted) in active markets that are accessible at the measurement date for assets or liabilities. The fair value hierarchy gives the highest priority to Level 1 inputs. • Level 2 - Observable prices that are based on inputs not quoted on active markets, but corroborated by market data. • Level 3 - Unobservable inputs are used when little or no market data is available. The fair value hierarchy gives the lowest priority to Level 3 inputs. Financial Liabilities that are not Measured at Fair Value on a Recurring Basis The following table presents certain information for our financial liability that is not measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Liabilities: Senior Notes $ 870,256 $ 882,379 $ 870,256 $ 883,580 Our long-term debt includes fixed rate debt. The fair value of this instrument is based on quoted market prices in markets that are not active. Therefore, this debt is classified as Level 2 within the fair value hierarchy. Financial Liabilities Measured at Fair Value on a Recurring Basis Contingent deferred acquisition consideration (Level 3 fair value measurement) is recorded at the acquisition date fair value and adjusted at each reporting period. The estimated liability is determined in accordance with various contractual valuation formulas and is dependent upon significant assumptions, such as the growth rate of the earnings of the relevant subsidiary during the contractual period and the discount rate. These growth rates are consistent with the Company’s long-term forecasts. As of March 31, 2021, the discount rate used to measure these liabilities was 5.1%. As these estimates require the use of assumptions about future performance, which are uncertain at the time of estimation, the fair value measurements presented on the Unaudited Condensed Consolidated Balance Sheets are subject to material uncertainty. See Note 5 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for additional information regarding contingent deferred acquisition consideration. At March 31, 2021 and December 31, 2020, the carrying amount of the Company’s financial instruments, including cash and cash equivalents, accounts receivable and accounts payable, approximated fair value because of their short-term maturity. Non-financial Assets and Liabilities that are Measured at Fair Value on a Nonrecurring Basis Certain non-financial assets are measured at fair value on a nonrecurring basis, primarily goodwill, intangible assets (Level 3 fair value measurement) and right-of-use lease assets (Level 2 fair value measurement). Accordingly, these assets are not measured and adjusted to fair value on an ongoing basis but are subject to periodic evaluations for potential impairment. The Company did not recognize an impairment of goodwill or intangible assets in the three months ended March 31, 2021. The company did not recognize an impairment of goodwill or intangible assets in the three months ended March 31, 2020.

Supplemental Information

Supplemental Information	3 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Information	Supplemental Information Impairment and Other Losses The Company recognized a charge of $875 for the three months ended March 31, 2021 to reduce the carrying value of two of its right-of-use lease assets and accelerate the operating expenses of one of its right-of-use lease assets. These right-of-use lease assets related to three agencies within its Integrated Networks - Group B reportable segment. See Note 6 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for additional information regarding the impairment of right-of-use lease assets and losses. Income Taxes Our tax provision for interim periods is determined using an estimated annual effective tax rate, adjusted for discrete items arising in interim periods. On March 27, 2020, the Coronavirus Aid, Relief, and Economic Security Act (the “CARES Act”) was signed into law. The CARES Act includes provisions relating to delaying certain payroll tax payments, refundable payroll tax credits, net operating loss carryback periods, modifications to the net interest deduction limitations and technical corrections to the tax depreciation methods for qualified improvement property. The tax law changes in the CARES Act did not have a material impact on the Company’s income tax provision. The Company had an income tax expense for the three months ended March 31, 2021 of $1,302 (on a pre-tax income of $11,296 resulting in an effective tax rate of 11.5%) compared to income tax expense of $13,500 (on pre-tax income of $15,293 resulting in an effective tax rate of 88.3%) for the three months ended March 31, 2020. The effective tax rate of 11.5% for the three months ended March 31, 2021 was primarily due to minimal tax expense recognized on U.S. earnings as a result of being subject to a valuation allowance.

Related Party Transactions

Related Party Transactions	3 Months Ended
	Mar. 31, 2021
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions In the ordinary course of business, the Company enters into transactions with related parties, including Stagwell and its affiliates. The transactions may range in the nature and value of services underlying the arrangements. Below are the related party transactions that are significant in nature: In October 2019, a Partner Firm of the Company entered into an arrangement with a Stagwell affiliate, in which the Stagwell affiliate and the Partner Firm collaborated to provide various services to a client of the Partner Firm. The Partner Firm and the Stagwell affiliate pitched and won this business together, with the client ultimately determining the general scope of work for each agency. Under the arrangement, which was structured as a sub-contract due to client preference, the Partner Firm is expected to pay the Stagwell affiliate, for services provided by the Stagwell affiliate in connection with serving the client, approximately $2,000 which has been fully recognized through March 31, 2021. As of March 31, 2021, $101 was owed to the affiliate. In January 2021, a Partner Firm of the Company entered into an arrangement with a certain Stagwell affiliate to perform media planning, buying and reporting services. Under the arrangement, the Partner Firm is expected to receive from the Stagwell affiliate approximately $529, which have been fully recognized through March 2021. As of March 31, 2021, $0 was due from the affiliate. In May 2020, a Partner Firm of the Company entered into an arrangement with a certain Stagwell affiliate to perform programmatic media planning, buying and reporting services. Under the arrangement, the Partner Firm is expected to receive from the Stagwell affiliate approximately $2,397, which is expected to be fully recognized in May 2021. As of March 31, 2021, $0 was due from the affiliate. In November 2020, a Partner Firm of the Company entered into an arrangement with a certain Stagwell affiliate to perform Event Management Services. Under the arrangement, the Partner Firm is expected to receive from the Stagwell affiliate approximately $456, which has been fully recognized as of March of 2021. As of March 31, 2021, $316 was due from the affiliate. In February 2021, a Partner Firm of the Company entered into an arrangement with a certain Stagwell affiliate to perform requirements gathering and concept features for a future-leaning ad platform for the augmented reality space. Under the arrangement, the Stagwell affiliate is expected to receive from the Partner Firm approximately $140, which will be recognized through April 2021. As of March 31, 2021, $140 was due to the affiliate. In March 2021, a Partner Firm of the Company entered into an arrangement with a certain Stagwell affiliate to perform media relations support and outreach services. Under the arrangement, the Partner Firm is expected to receive from the Stagwell affiliate approximately $190, which will be recognized through September 2022. As of March 31, 2021, $10 was due from the affiliate.

Segment Information

Segment Information	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segment Information	Segment Information The Company determines an operating segment if a component (i) engages in business activities from which it earns revenues and incurs expenses, (ii) has discrete financial information, and is (iii) regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is Mark Penn, Chief Executive Officer and Chairman, to make decisions regarding resource allocation for the segment and assess its performance. Once operating segments are identified, the Company performs an analysis to determine if aggregation of operating segments is applicable. This determination is based upon a quantitative analysis of the expected and historic average long-term profitability for each operating segment, together with a qualitative assessment to determine if operating segments have similar operating characteristics. The CODM uses Adjusted EBITDA (defined below) as a key metric, to evaluate the operating and financial performance of a segment, identify trends affecting the segments, develop projections and make strategic business decisions. Adjusted EBITDA is defined as Net income (loss) attributable to MDC Partners Inc. common shareholders’ plus or minus non-operating items to operating income (loss), plus depreciation and amortization, stock-based compensation, deferred acquisition consideration adjustments, distributions from non-consolidated affiliates and other items, net. Distributions from non-consolidated affiliates includes (i) cash received for profit distributions from non-consolidated affiliates, and (ii) consideration from the sale of ownership interests in non-consolidated affiliates, less contributions to date, plus undistributed earnings (losses). Other items, net includes items such as merger related costs, severance and other restructuring expenses , including costs for leases that will either be terminated or sublet in connection with the centralization of our New York real estate portfolio. The three reportable segments that result from applying the aggregation criteria are as follows: “Integrated Networks - Group A,” “Integrated Networks - Group B” and the “Media & Data Network.” In addition, the Company combines and discloses operating segments that do not meet the aggregation criteria as “All Other.” The Company also reports corporate expenses, as further detailed below, as “Corporate.” All segments follow the same basis of presentation and accounting policies as those described throughout the Notes to the Unaudited Condensed Consolidated Financial Statements included herein and Note 2 of the Company’s 2020 Form 10-K. • The Integrated Networks - Group A reportable segment is comprised of the Anomaly Alliance (Anomaly, Concentric Partners, Hunter, Mono, Y Media Labs) and Colle McVoy operating segments. • The Integrated Networks - Group B reportable segment is comprised of the Constellation (72andSunny, CPB, Instrument and Redscout) and Doner Partner Network (6degrees, Doner, KWT, Union, Veritas and Yamamoto) operating segments. The operating segments aggregated within the Integrated Networks - Group A and B reportable segments provide a range of services for their clients, primarily including strategy, creative and production for advertising campaigns across a variety of platforms (print, digital, social media, television broadcast) as well as public relations and communications services, experiential, social media and influencer marketing. These operating segments share similar characteristics related to (i) the nature of their services; (ii) the type of clients and the methods used to provide services; and (iii) the extent to which they may be impacted by global economic and geopolitical risks. In addition, these operating segments compete with each other for new business and from time to time have business move between them. While the operating segments are similar in nature, the distinction between the Integrated Networks - Group A and B is the aggregation of operating segments that have the most similar historical and expected average long-term profitability. • The Media & Data Network reportable segment is comprised of a single operating segment that combines media buying and planning across a range of platforms (out-of-home, paid search, social media, lead generation, programmatic, television broadcast) with technology and data capabilities. The Media & Data Network includes Gale Partners, Kenna, MDC Media and Northstar. • All Other consists of the Company’s remaining operating segments that provide a range of services including advertising, public relations and marketing communication services, but generally do not have similar services offerings or financial characteristics as those aggregated in the reportable segments. The All Other category includes Allison & Partners, Bruce Mau, Forsman & Bodenfors, Hello, Team and Vitro. • Corporate consists of corporate office expenses incurred in connection with the strategic resources provided to the operating segments, as well as certain other centrally managed expenses that are not fully allocated to the operating segments. These office and general expenses include (i) salaries and related expenses for corporate office employees, including employees dedicated to supporting the operating segments, (ii) occupancy expenses relating to properties occupied by all corporate office employees, (iii) other office and general expenses including professional fees for the financial statement audits and other public company costs, and (iv) certain other professional fees managed by the corporate office. Additional expenses managed by the corporate office that are directly related to the operating segments are allocated to the appropriate reportable segment and the All Other category. Three Months Ended March 31, 2021 2020 Revenue: (Dollars in Thousands) Integrated Networks - Group A $ 102,386 $ 90,621 Integrated Networks - Group B 111,151 117,707 Media & Data Network 36,783 41,058 All Other 57,265 78,356 Total $ 307,585 $ 327,742 Adjusted EBITDA: Integrated Networks - Group A $ 22,462 $ 16,301 Integrated Networks - Group B 25,869 17,136 Media & Data Network 5,081 1,787 All Other 6,042 9,904 Corporate (7,520) (5,562) Total Adjusted EBITDA $ 51,934 $ 39,566 Depreciation and amortization $ (8,176) $ (9,206) Impairment and other losses (875) (161) Stock-based compensation 1,963 (3,070) Deferred acquisition consideration (11,685) 4,600 Distributions from non-consolidated affiliates (9) 14 Other items, net (5,485) (2,416) Total Operating Income $ 27,667 $ 29,327 Other Income (expenses): Interest expense and finance charges, net $ (19,065) $ (15,611) Foreign exchange gain (loss) 2,080 (14,757) Other, net 614 16,334 Income before income taxes and equity in earnings of non-consolidated affiliates 11,296 15,293 Income tax expense 1,302 13,500 Income before equity in earnings of non-consolidated affiliates 9,994 1,793 Equity in losses of non-consolidated affiliates (493) — Net income 9,501 1,793 Net income attributable to the noncontrolling interest (4,491) (791) Net income attributable to MDC Partners Inc. 5,010 1,002 Accretion on and net income allocated to convertible preference shares (4,089) (3,440) Net income (loss) attributable to MDC Partners Inc. common shareholders $ 921 $ (2,438) Three Months Ended March 31, 2021 2020 Depreciation and amortization: (Dollars in Thousands) Integrated Networks - Group A $ 1,294 $ 1,741 Integrated Networks - Group B 3,657 4,526 Media & Data Network 472 808 All Other 1,537 1,899 Corporate 1,216 232 Total $ 8,176 $ 9,206 Stock-based compensation: Integrated Networks - Group A $ (3,628) $ 1,961 Integrated Networks - Group B 953 900 Media & Data Network 21 (13) All Other 61 80 Corporate 630 142 Total $ (1,963) $ 3,070 Capital expenditures: Integrated Networks - Group A $ 275 $ 358 Integrated Networks - Group B 213 477 Media & Data Network 64 85 All Other 134 324 Corporate (170) 302 Total $ 516 $ 1,546 The Company’s CODM does not use segment assets to allocate resources or to assess performance of the segments and therefore, total segment assets have not been disclosed. See Note 3 of the Notes to the Unaudited Condensed Consolidated Financial Statements included herein for a summary of the Company’s revenue by geographic region for the three months ended March 31, 2021 and 2020.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2021
By Location
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	The following table presents revenue disaggregated by geography for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, Geographical Location Reportable Segment 2021 2020 United States All $242,580 $264,561 Canada All 22,650 18,256 Other All 42,355 44,925 $307,585 $327,742
Industry Vertical
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	The following table presents revenue disaggregated by client industry vertical for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, Industry Reportable Segment 2021 2020 Food & Beverage All $ 55,178 $ 58,091 Retail All 30,777 36,303 Consumer Products All 45,405 39,769 Communications All 16,990 41,045 Automotive All 15,629 25,192 Technology All 46,390 25,535 Healthcare All 31,494 24,066 Financials All 24,442 24,005 Transportation and Travel/Lodging All 9,948 20,486 Other All 31,332 33,250 $ 307,585 $ 327,742

Income (Loss) Per Common Share

Income (Loss) Per Common Share (Tables)	3 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share	The following table sets forth the computation of basic and diluted income (loss) per common share: Three Months Ended March 31, 2021 2020 Numerator: Net income attributable to MDC Partners Inc. $ 5,010 $ 1,002 Accretion on convertible preference shares (3,724) (3,440) Net income allocated to convertible preference shares (365) — Net income (loss) attributable to MDC Partners Inc. common shareholders $ 921 $ (2,438) Adjustment to net income allocated to convertible preference shares 7 — Net income (loss) attributable to MDC Partners Inc. common shareholders - Diluted $ 928 $ (2,438) Denominator: Basic weighted average number of common shares outstanding 73,392,824 72,397,661 Diluted weighted average number of common shares outstanding 75,439,066 72,397,661 Basic $ 0.01 $ (0.03) Diluted $ 0.01 $ (0.03)

Deferred Acquisition Consider_2

Deferred Acquisition Consideration (Tables)	3 Months Ended
	Mar. 31, 2021
Business Combinations [Abstract]
Schedule of Changes in Contingent Deferred Acquisition Consideration	The following table presents changes in contingent deferred acquisition consideration, which is measured at fair value on a recurring basis using significant unobservable inputs, and a reconciliation to the amounts reported on the balance sheets as of March 31, 2021 and December 31, 2020. March 31, December 31, 2021 2020 Beginning Balance of Contingent Payments $ 82,802 $ 74,671 Payments (1,153) (46,792) Redemption value adjustments (1) 12,392 44,993 Additions - Acquisitions and step-up transactions — 7,703 Other (641) 2,227 Ending balance of contingent payments $ 93,400 $ 82,802 Fixed Payments — 263 $ 93,400 $ 83,065 (1) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments and stock-based compensation charges relating to acquisition payments that are tied to continued employment. Redemption value adjustments are recorded within Office and general expenses on the Unaudited Condensed Consolidated Statements of Operations. The following table presents the impact to the Company’s Statements of operations due to the redemption value adjustments for the contingent deferred acquisition consideration: Three Months Ended March 31, 2021 2020 Loss (income) attributable to fair value adjustments $ 11,685 $ (4,600) Stock-based compensation 707 2,025 Redemption value adjustments $ 12,392 $ (2,575)

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2021
Leases [Abstract]
Lease Costs and Other Quantitative Information	The following table presents lease costs and other quantitative information for the three months ended March 31, 2021 and 2020: Three Months Ended March 31, 2021 2020 Lease Cost: Operating lease cost $ 17,127 $ 16,391 Variable lease cost 2,593 4,655 Sublease rental income (2,564) (2,805) Total lease cost $ 17,156 $ 18,241 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 16,796 $ 17,635 Right-of-use lease assets obtained in exchange for operating lease liabilities and other non-cash adjustments $ 3,816 $ 7,119 Weighted average remaining lease term (in years) - Operating leases 7.2 7.0 Weighted average discount rate - Operating leases 10.6 8.7
Minimum Future Rental Payments	The following table presents minimum future rental payments under the Company’s leases at March 31, 2021 and their reconciliation to the corresponding lease liabilities: Maturity Analysis Remaining 2021 $52,871 2022 61,447 2023 56,839 2024 50,615 2025 39,582 2026 and thereafter 152,702 Total 414,056 Less: Present value discount (131,452) Lease liability $ 282,604

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Debt	March 31, 2021 December 31, 2020 Revolving Credit Agreements $ 20,000 $ — Senior Notes 870,256 870,256 Debt Issuance Cost (25,406) (27,072) $ 864,850 $ 843,184

Noncontrolling and Redeemable_2

Noncontrolling and Redeemable Noncontrolling Interests (Tables)	3 Months Ended
	Mar. 31, 2021
Noncontrolling Interest [Abstract]
Change In Noncontrolling Interest [Table Text Block]	Changes in amounts due to noncontrolling interest holders included in Accruals and other liabilities on the Unaudited Condensed Consolidated Balance Sheets for the year ended December 31, 2020 and three months ended March 31, 2021 were as follows: Noncontrolling Balance at December 31, 2019 $ 14,028 Income attributable to noncontrolling interests 21,774 Distributions made (15,192) Other 94 Balance at December 31, 2020 $ 20,704 Income attributable to noncontrolling interests 4,491 Distributions made (5,285) Other 36 Balance at March 31, 2021 $ 19,946
Noncontrolling Interest [Table Text Block]	Changes in the Company’s ownership interests in our less than 100% owned subsidiaries during the three months ended March 31, 2021 and 2020 were as follows: Three Months Ended March 31, 2021 2020 Net income attributable to MDC Partners Inc. $ 5,010 $ 1,002 Transfers from the noncontrolling interest: Decrease in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests (330) (503) Net transfers from noncontrolling interests $ (330) $ (503) Change from Net income attributable to MDC Partners Inc. and transfers to noncontrolling interests $ 4,680 $ 499
Redeemable Noncontrolling Interest [Table Text Block]	The following table presents changes in redeemable noncontrolling interests: Three Months Ended March 31, 2021 Year Ended December 31, 2020 Beginning Balance $ 27,137 $ 36,973 Redemptions — (12,289) Granted — — Changes in redemption value (1,681) 2,800 Currency translation adjustments (104) (347) Ending Balance $ 25,352 $ 27,137

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Liability Measured on a Non-recurring Basis	The following table presents certain information for our financial liability that is not measured at fair value on a recurring basis at March 31, 2021 and December 31, 2020: March 31, 2021 December 31, 2020 Carrying Fair Value Carrying Fair Value Liabilities: Senior Notes $ 870,256 $ 882,379 $ 870,256 $ 883,580

Segment Information (Tables)

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Three Months Ended March 31, 2021 2020 Revenue: (Dollars in Thousands) Integrated Networks - Group A $ 102,386 $ 90,621 Integrated Networks - Group B 111,151 117,707 Media & Data Network 36,783 41,058 All Other 57,265 78,356 Total $ 307,585 $ 327,742 Adjusted EBITDA: Integrated Networks - Group A $ 22,462 $ 16,301 Integrated Networks - Group B 25,869 17,136 Media & Data Network 5,081 1,787 All Other 6,042 9,904 Corporate (7,520) (5,562) Total Adjusted EBITDA $ 51,934 $ 39,566 Depreciation and amortization $ (8,176) $ (9,206) Impairment and other losses (875) (161) Stock-based compensation 1,963 (3,070) Deferred acquisition consideration (11,685) 4,600 Distributions from non-consolidated affiliates (9) 14 Other items, net (5,485) (2,416) Total Operating Income $ 27,667 $ 29,327 Other Income (expenses): Interest expense and finance charges, net $ (19,065) $ (15,611) Foreign exchange gain (loss) 2,080 (14,757) Other, net 614 16,334 Income before income taxes and equity in earnings of non-consolidated affiliates 11,296 15,293 Income tax expense 1,302 13,500 Income before equity in earnings of non-consolidated affiliates 9,994 1,793 Equity in losses of non-consolidated affiliates (493) — Net income 9,501 1,793 Net income attributable to the noncontrolling interest (4,491) (791) Net income attributable to MDC Partners Inc. 5,010 1,002 Accretion on and net income allocated to convertible preference shares (4,089) (3,440) Net income (loss) attributable to MDC Partners Inc. common shareholders $ 921 $ (2,438) Three Months Ended March 31, 2021 2020 Depreciation and amortization: (Dollars in Thousands) Integrated Networks - Group A $ 1,294 $ 1,741 Integrated Networks - Group B 3,657 4,526 Media & Data Network 472 808 All Other 1,537 1,899 Corporate 1,216 232 Total $ 8,176 $ 9,206 Stock-based compensation: Integrated Networks - Group A $ (3,628) $ 1,961 Integrated Networks - Group B 953 900 Media & Data Network 21 (13) All Other 61 80 Corporate 630 142 Total $ (1,963) $ 3,070 Capital expenditures: Integrated Networks - Group A $ 275 $ 358 Integrated Networks - Group B 213 477 Media & Data Network 64 85 All Other 134 324 Corporate (170) 302 Total $ 516 $ 1,546

Basis of Presentation and Rec_2

Basis of Presentation and Recent Developments (Details)	3 Months Ended
	Mar. 31, 2021reportable_segment	Mar. 23, 2016USD ($)
Debt [Line Items]
Number of reportable segments | reportable_segment	3
6.50% Notes due 2024
Debt [Line Items]
Interest rate, stated percentage	7.50%
6.50% Notes due 2024 | Senior Notes
Debt [Line Items]
Aggregate principal amount | $		$ 900,000,000

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details Textual) - USD ($) $ in Thousands	Jul. 01, 2020	Mar. 19, 2020	Feb. 14, 2020	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Aggregate purchase price for noncontrolling interest				$ 5,486	$ 4,608
Deferred acquisition consideration				93,400		$ 83,065
Redeemable noncontrolling interest, redemptions, value				0		$ 12,289
Veritas [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired	10.00%
Aggregate purchase price for noncontrolling interest	$ 2,187
Deferred cash payment for noncontrolling interest	1,087
Reduction of noncontrolling and redeemable noncontrolling interest	2,651
Difference between purchase price and noncontrolling interest recorded in common stock and other paid-in capital	$ 464
KWT Global [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)		22.50%
Aggregate purchase price		$ 2,118
Closing cash payment		729
Deferred acquisition consideration		1,389
Redeemable noncontrolling interest, redemptions, value				$ (1,615)
Reduction in noncontrolling interests		$ 503
Sloane and Company LLC [Member]
Business Acquisition [Line Items]
Proceeds from Divestiture of Businesses			$ 26,696
Gain (loss) on disposition of business			$ 16,827
Sloane and Company LLC [Member] | Disposal Group, Disposed of by Sale, Not Discontinued Operations [Member]
Business Acquisition [Line Items]
Period of contingent payments expected after disposal			2 years

Revenue - Additional Informatio

Revenue - Additional Information (Details)	3 Months Ended
	Mar. 31, 2021country
Non-US And Canada [Member]
Disaggregation of Revenue [Line Items]
Number of countries in which entity operates	11
Minimum
Disaggregation of Revenue [Line Items]
Payment period	30 days
Termination period	30 days
Maximum
Disaggregation of Revenue [Line Items]
Payment period	60 days
Termination period	90 days

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Services	$ 307,585	$ 327,742
United States
Disaggregation of Revenue [Line Items]
Services	242,580	264,561
Canada
Disaggregation of Revenue [Line Items]
Services	22,650	18,256
Other
Disaggregation of Revenue [Line Items]
Services	42,355	44,925
Food & Beverage
Disaggregation of Revenue [Line Items]
Services	55,178	58,091
Retail
Disaggregation of Revenue [Line Items]
Services	30,777	36,303
Consumer Products
Disaggregation of Revenue [Line Items]
Services	45,405	39,769
Communications
Disaggregation of Revenue [Line Items]
Services	16,990	41,045
Automotive
Disaggregation of Revenue [Line Items]
Services	15,629	25,192
Technology
Disaggregation of Revenue [Line Items]
Services	46,390	25,535
Healthcare
Disaggregation of Revenue [Line Items]
Services	31,494	24,066
Financials
Disaggregation of Revenue [Line Items]
Services	24,442	24,005
Transportation and Travel/Lodging
Disaggregation of Revenue [Line Items]
Services	9,948	20,486
Other
Disaggregation of Revenue [Line Items]
Services	$ 31,332	$ 33,250

Revenue - Contract Assets and L

Revenue - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Unbilled service fees	$ 59,143	$ 49,110
Unbilled outside vendor costs, billable to clients	22,824	10,552
Contract with Customer, Liability, Revenue Recognized		69,699
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, amount	5,799
Advance Billings
Disaggregation of Revenue [Line Items]
Advance billings	170,159	152,956
Increase (Decrease) in Contract with Customer, Liability	17,203
Contract with Customer, Liability, Revenue Recognized	$ 99,188
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Percentage	83.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Revenue, Remaining Performance Obligation, Percentage	17.00%
Accrued Expenses and Other Current Liabilities
Disaggregation of Revenue [Line Items]
Advance billings	$ 97,075	$ 112,755
Increase (Decrease) in Contract with Customer, Liability	$ 15,680

Income (Loss) Per Common Shar_2

Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Class of Stock [Line Items]
Net loss attributable to MDC Partners Inc.	$ 5,010	$ 1,002
Numerator
Net income (loss) attributable to MDC Partners Inc. common shareholders	$ 921	$ (2,438)
Denominator
Denominator for basic income (loss) per common share - weighted average common shares	73,392,824	72,397,661,000
Denominator for diluted income (loss) per common share - adjusted weighted shares and assumed conversions	75,439,066	72,397,661,000
Earnings per share, basic	$ 0.01	$ (0.03)
Earnings per share, diluted	$ 0.01	$ (0.03)
Series 4 Convertible Preferred Stock | Convertible Preference Shares
Numerator
Accretion on and net income allocated to convertible preference shares	$ (3,724)
Net income allocated to convertible preference shares	$ (365)	$ 0
Denominator
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	1,920,634	2,835,770

Income (Loss) Per Common Shar_3

Income (Loss) Per Common Share (Details Textual) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Contingent Restricted Stock Units (RSUs)
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	0	2,203,717
Series 4 Convertible Preferred Stock | Convertible Preference Shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share (shares)	1,920,634	2,835,770
Shares outstanding (shares)	145,000,000	145,000,000	145,000,000	145,000,000
Convertible preferred stock, common shares issuable upon conversion (shares)	29,430,693	27,189,411

Deferred Acquisition Consider_3

Deferred Acquisition Consideration (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments	$ 82,802	$ 74,671	$ 74,671
Payments	1,153		46,792
Redemption value adjustments	12,392	(2,575)	44,993
Additions	0		7,703
Foreign translation adjustment	(641)		2,227
Ending balance of contingent payments	93,400		82,802
Deferred acquisition consideration	93,400		83,065
Stock-based compensation	707	2,025
Fixed payments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deferred acquisition consideration	0		$ 263
Contingent Payment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Loss (income) attributable to fair value adjustments	$ 11,685	$ (4,600)

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)lease
Leases [Abstract]
Number of leases not yet commenced | lease	5
Leases not yet commenced, liability	$ 34,020
Impairment of right-of-use asset and accelerated operating expenses	$ 875

Leases - Lease Costs and Other

Leases - Lease Costs and Other Quantitative Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Leases [Abstract]
Operating lease cost	$ 17,127	$ 16,391
Variable lease cost	2,593	4,655
Sublease rental income	(2,564)	(2,805)
Total lease cost	17,156	18,241
Operating cash flows	16,796	17,635
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 3,816	$ 7,119
Weighted average remaining lease term (in years) - Operating leases	7 years 2 months 12 days	7 years
Weighted average discount rate - Operating leases	10.60%	870.00%

Leases - Minimum Future Rental

Leases - Minimum Future Rental Payments (Details) $ in Thousands	Mar. 31, 2021USD ($)
Leases [Abstract]
Remaining 2021	$ 52,871
2022	61,447
2023	56,839
2024	50,615
2025	39,582
2026 and thereafter	152,702
Total	414,056
Less: Present value discount	(131,452)
Lease liability	$ 282,604

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt [Line Items]
Revolving credit agreement	$ 20,000	$ 0
Debt Issuance Cost	(25,406)	(27,072)
Long-term Debt, Excluding Current Maturities	864,850	843,184
6.50% Notes due 2024 | Fair Value, Inputs, Level 1 | Senior Notes
Debt [Line Items]
Long-term Debt	$ 870,256	$ 870,256

Debt (Details Textual)

Debt (Details Textual) - USD ($)	May 28, 2020	Mar. 23, 2016	Mar. 31, 2021	Dec. 31, 2020
Debt [Line Items]
Amount outstanding under the line of credit			$ 20,000,000	$ 0
Prime Rate | Minimum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.75%
Prime Rate | Maximum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%
Non-Prime Rate | Minimum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Non-Prime Rate | Maximum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
6.50% Notes due 2024
Debt [Line Items]
Interest rate, stated percentage			7.50%
Senior Notes | 6.50% Notes due 2024
Debt [Line Items]
Aggregate principal amount		$ 900,000,000
Percentage of redemption price, change in ownership controllatest for redemption at face amount		101.00%
Percentage of redemption price, redemption date, latest for redemption at face amounttion Price, Redemption Date, Latest For Redemption At Face Amount		100.00%
Line of Credit [Member]
Debt [Line Items]
Maximum borrowing capacity			$ 211,500,000
Letter of Credit
Debt [Line Items]
Maximum borrowing capacity			$ 19,151,000	$ 18,651,000

Noncontrolling and Redeemable_3

Noncontrolling and Redeemable Noncontrolling Interests (Details Textual) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 25,352	$ 27,137	$ 36,973
Vesting over period [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	16,469
Termination, disability, or death [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	8,883
Acquisition Value in excess of Redemption Value [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 0

Noncontrolling and Redeemable_4

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Amounts Due to Noncontrolling Interest (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Noncontrolling Interest [Abstract]
Beginning balance	$ 20,704	$ 14,028
Income attributable to noncontrolling interests		21,774
Distributions made	(5,285)	(15,192)
Other	36	$ 94
Ending balance	$ 19,946

Noncontrolling and Redeemable_5

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.	$ 5,010	$ 1,002
Business acquisitions and step-up transactions, net of tax	(330)	(503)
Change from Net income attributable to MDC Partners Inc. and transfers to noncontrolling interests	(4,680)	(499)
MDC Partners Inc. Shareholders' Deficit
Noncontrolling Interest [Line Items]
Business acquisitions and step-up transactions, net of tax	$ (330)	$ (503)

Noncontrolling and Redeemable_6

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Noncontrolling Interest [Abstract]
Beginning Balance	$ 27,137	$ 36,973
Redemptions	0	12,289
Granted	0	0
Changes in redemption value	1,681	(2,800)
Currency translation adjustments	(104)	(347)
Ending Balance	$ 25,352	$ 27,137

Share Capital (Details Textual)

Share Capital (Details Textual)	Mar. 14, 2019USD ($)$ / sharesshares	Mar. 07, 2017USD ($)$ / shares	Mar. 31, 2021USD ($)vote$ / sharesshares	Dec. 31, 2020USD ($)shares	Mar. 31, 2020USD ($)shares	Dec. 31, 2019USD ($)shares
Share Capital [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ (405,583,000)	$ (408,910,000)	$ (183,944,000)	$ (190,575,000)
Preferred Stock
Share Capital [Line Items]
Proceeds from Issuance of Convertible Preferred Stock	$ 98,620,000
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest		$ 90,123,000	$ 152,746,000	$ 152,746,000	$ 152,746,000	$ 152,746,000
Preferred Stock | Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Proceeds from Issuance of Convertible Preferred Stock		$ 95,000
Preferred Stock, Conversion Price Per Preference Share | $ / shares	$ 7.42	$ 10
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Accretion Rate, Preference Per Share | $ / shares			$ 9.02
Preferred Stock, Accretion of Redemption Discount			$ 2,571,000
Preferred Stock, Liquidation Preference, Value			$ 131,110,000
Preferred Stock, Convertible Preference Shares, Convertible at Company's Option, Term	2 years	5 years
Shares outstanding (shares) | shares			145,000,000	145,000,000	145,000,000	145,000,000
Preferred Stock, Conversion Basis, Common Stock Class A Closing Trade Price	125.00%
Preferred Stock, Liquidation Preference Percentage Rate, Change of Control of the Company	7.00%
Preferred Stock | Series 6 Convertible Preferred Stock
Share Capital [Line Items]
Stock Issued During Period, Shares, Issued for Services | shares	50,000
Proceeds from Issuance of Convertible Preferred Stock	$ 50,000,000
Preferred Stock, Liquidation Preference Per Share | $ / shares	$ 1,000	$ 1,000
Preferred Stock, Conversion Price Per Preference Share | $ / shares	$ 5
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Monthly Accretion of Redemption Discount			$ 7.69
Preferred Stock, Accretion of Redemption Discount			1,153,000
Preferred Stock, Liquidation Preference, Value			58,804,000
Preferred Stock, Convertible Preference Shares, Convertible at Company's Option, Term	2 years	5 years
Preferred Stock, Conversion Basis, Common Stock Class A Closing Trade Price	125.00%
Preferred Stock, Dividend Rate, Percentage	7.00%
Common Stock and Other Paid-in Capital
Share Capital [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			$ 106,193,000	$ 104,367,000	$ 99,587,000	$ 101,469,000
Issuance of common and convertible preference shares	$ 35,997
Common Shares | Common Class A
Share Capital [Line Items]
Stock Issued During Period, Shares, Issued for Services | shares	14,285,714
Proceeds from Issuance of Common Stock	$ 50,000,000
Shares outstanding (shares) | shares			74,787,317	73,529,105
Common stock, voting rights, number of votes per share | vote			1
Common Stock, Par or Stated Value Per Share | $ / shares			$ 0
Common Shares | Common Class B
Share Capital [Line Items]
Shares outstanding (shares) | shares			3,743	3,743
Common stock, voting rights, number of votes per share | vote			20
Preferred Stock, Par or Stated Value Per Share | $ / shares			$ 0
Contingent Consideration, Liability Settlements [Domain] | Preferred Stock | Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Issuance of common and convertible preference shares	$ 62,623

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)
Liabilities:
Impairment of right-of-use asset	$ 598
Measurement Input, Discount Rate
Liabilities:
Business Combination, Contingent Consideration, Liability, Measurement Input	0.051
Senior Notes | Reported Value Measurement
Liabilities:
Debt Instrument, Fair Value Disclosure	$ 870,256	$ 870,256
Senior Notes | Estimate of Fair Value Measurement
Liabilities:
Debt Instrument, Fair Value Disclosure	882,379	883,580
6.50% Notes due 2024 | Fair Value, Inputs, Level 1 | Senior Notes
Liabilities:
Long term debt, Carrying Amount	$ 870,256	$ 870,256

Supplemental Information (Detai

Supplemental Information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Asset Impairment Charges	$ 875	$ 161
Impairment of Right-Of-Use Asset	598
Goodwill	669,060		$ 668,211
Income tax expense	1,302	13,500
Income before income taxes and equity in earnings of non-consolidated affiliates	$ 11,296	$ 15,293
Effective tax rate (percent)	11.50%	88.30%
Revenues	$ 307,585	$ 327,742
Increase (Decrease) in Accounts Receivable	$ 2,779	$ (41,148)

Supplemental Information - Stat

Supplemental Information - Statements of Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Revenues	$ 307,585	$ 327,742
Asset Impairment Charges	875	161
Costs and Expenses	279,918	298,415
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	11,296	15,293
Income Tax Expense (Benefit)	1,302	13,500
Net income (loss) attributable to MDC Partners Inc. common shareholders	$ 921	$ (2,438)
Weighted Average Number of Shares Outstanding, Basic	73,392,824	72,397,661,000
Weighted Average Number of Shares Outstanding, Diluted	75,439,066	72,397,661,000
Income (Loss) from Continuing Operations, Per Basic Share	$ 0.01	$ (0.03)
Income (Loss) from Continuing Operations, Per Diluted Share	$ 0.01	$ (0.03)

Supplemental Information - Bala

Supplemental Information - Balance Sheets (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Accounts Receivable, after Allowance for Credit Loss, Current	$ 377,670	$ 374,892
Goodwill	669,060	668,211
Assets	1,560,713	1,511,312
Accruals and other liabilities	242,667	274,968
Liabilities	1,940,944	1,893,085
Accumulated deficit	(704,741)	(709,751)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(405,583)	(408,910)	$ (183,944)	$ (190,575)
Liabilities and Equity	$ 1,560,713	$ 1,511,312

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021
Related Party Transaction [Line Items]
Sublease rental income		$ 2,564	$ 2,805
Stagwell Subsidiary [Member] | Services Provided By Subisidiary [Member]
Related Party Transaction [Line Items]
Due to Related Parties		2,000		$ 2,000
Accounts Payable, Related Parties		101		101
Stagwell Subsidiary [Member] | Event Management Services
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction				456
Due from Related Parties		316		316
Stagwell Affiliate [Member] | Affiliated Entity [Member] | Arrangement To Perform Media, Planning, Buying And Reporting Services [Member]
Related Party Transaction [Line Items]
Accounts receivable, related parties, current		529		529
Due from (to) from related parties		$ 0		$ 0
Other Company [Member] | Board of Directors Chairman [Member]
Related Party Transaction [Line Items]
Sublease rental income	$ 65

Segment Information (Details 1)

Segment Information (Details 1) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)reportable_segment	Mar. 31, 2020USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment	3
Revenues	$ 307,585	$ 327,742
Segment operating income (loss)	27,667	29,327
Interest expense and finance charges, net	(19,065)	(15,611)
Foreign exchange gain (loss)	2,080	(14,757)
Other, net	614	16,334
Income before income taxes and equity in earnings of non-consolidated affiliates	11,296	15,293
Income tax expense	1,302	13,500
Income before equity in earnings of non-consolidated affiliates	9,994	1,793
Equity in losses of non-consolidated affiliates	(493)	0
Net income	9,501	1,793
Net income attributable to the noncontrolling interest	(4,491)	(791)
Net income attributable to MDC Partners Inc.	5,010	1,002
Net income (loss) attributable to MDC Partners Inc. common shareholders	921	(2,438)
Asset Impairment Charges	(875)	(161)
Depreciation, Depletion and Amortization, Nonproduction	8,176	9,206
Depreciation	8,176	9,206
Stock-based compensation	1,963	(3,070)
Proceeds from (Payments to) Noncontrolling Interests	(9)	14
Deferred acquisition consideration	(11,685)	4,600
Other Operating Income	(5,485)	(2,416)
Adjusted EBITDA	51,934	39,566
Capital Expenditures, Incurred, Paid and Not Yet Paid	516	1,546
Series 4 Convertible Preferred Stock [Domain] | Convertible Preference Shares
Segment Reporting Information [Line Items]
Accretion on and net income allocated to convertible preference shares	4,089	3,440
All Other
Segment Reporting Information [Line Items]
Revenues	57,265	78,356
Depreciation, Depletion and Amortization, Nonproduction	1,537	1,899
Stock-based compensation	(61)	(80)
Adjusted EBITDA	6,042	9,904
Capital Expenditures, Incurred, Paid and Not Yet Paid	134	324
Media And Data Network
Segment Reporting Information [Line Items]
Revenues	36,783	41,058
Depreciation, Depletion and Amortization, Nonproduction	472	808
Stock-based compensation	(21)	13
Adjusted EBITDA	5,081	1,787
Capital Expenditures, Incurred, Paid and Not Yet Paid	64	85
Integrated Networks - Group A
Segment Reporting Information [Line Items]
Revenues	102,386	90,621
Depreciation, Depletion and Amortization, Nonproduction	1,294	1,741
Stock-based compensation	3,628	(1,961)
Adjusted EBITDA	22,462	16,301
Capital Expenditures, Incurred, Paid and Not Yet Paid	275	358
Integrated Networks - Group B
Segment Reporting Information [Line Items]
Revenues	111,151	117,707
Depreciation, Depletion and Amortization, Nonproduction	3,657	4,526
Stock-based compensation	(953)	(900)
Adjusted EBITDA	25,869	17,136
Capital Expenditures, Incurred, Paid and Not Yet Paid	213	477
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Depreciation, Depletion and Amortization, Nonproduction	1,216	232
Stock-based compensation	(630)	(142)
Adjusted EBITDA	(7,520)	(5,562)
Capital Expenditures, Incurred, Paid and Not Yet Paid	$ (170)	$ 302