Stagwell (STGW) 10-K 16 Mar 21 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 25, 2021
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
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
Entity Address, Address Line Two	Floor 65
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10007
City Area Code	646
Local Phone Number	429-1800
Title of 12(b) Security	Class A Subordinate Voting Shares, no par value
Trading Symbol	MDCA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
Icfr Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float	$ 120
Documents Incorporated by Reference	Portions of the Registrant’s Proxy Statement relating to the 2021 Annual General Meeting of Stockholders are incorporated by reference in Part III of this Annual Report on Form 10-K where indicated.
Entity Central Index Key	0000876883
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false
Common Class A | Common Shares
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		73,722,720
Common Class B | Common Shares
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		3,743

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Services	$ 1,199,011	$ 1,415,803	$ 1,475,088
Operating expenses:
Cost of services sold	769,899	961,076	991,198
Office and general expenses	341,565	328,339	349,056
Depreciation and amortization	36,905	38,329	46,196
Impairment and other losses	96,399	8,599	87,204
Costs and Expenses, Total	1,244,768	1,336,343	1,473,654
Operating income (loss)	(45,757)	79,460	1,434
Other income (expense):
Interest expense and finance charges, net	(62,163)	(64,942)	(67,075)
Foreign exchange gain (loss)	(982)	8,750	(23,258)
Other, net	20,500	(2,401)	230
Nonoperating Income (Expense), Total	(42,645)	(58,593)	(90,103)
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	(88,402)	20,867	(88,669)
Income tax expense	116,555	10,316	29,615
Income (loss) before equity in earnings of non-consolidated affiliates	(204,957)	10,551	(118,284)
Equity in earnings (losses) of non-consolidated affiliates	(2,240)	352	62
Net income (loss)	(207,197)	10,903	(118,222)
Net income attributable to the noncontrolling interest	(21,774)	(16,156)	(11,785)
Net loss attributable to MDC Partners Inc.	(228,971)	(5,253)	(130,007)
Net loss attributable to MDC Partners Inc. common shareholders	$ (243,150)	$ (17,557)	$ (138,362)
Basic and diluted
Earnings per share, basic	$ (3.34)	$ (0.25)	$ (2.42)
Earnings per share, diluted	$ (3.34)	$ (0.25)	$ (2.42)
Weighted Average Number of Common Shares Outstanding:
Weighted Average Number of Shares Outstanding, Basic	72,862,178	69,132,100	57,218,994
Weighted Average Number of Shares Outstanding, Diluted	72,862,178	69,132,100	57,218,994
Series 4 Convertible Preferred Stock | Convertible Preference Shares
Other income (expense):
Accretion on and net income allocated to convertible preference shares	$ (14,179)	$ (12,304)	$ (8,355)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Comprehensive income (loss)
Net loss	$ (207,197)	$ 10,903	$ (118,222)
Other comprehensive income (loss), net of applicable tax:
Foreign currency translation adjustment	9,092	(6,691)	3,158
Benefit plan adjustment, net of income tax expense (benefit) of ($519) for 2020, ($740) for 2019 and $223 for 2018	(1,354)	(1,911)	555
Other comprehensive income (loss)	7,738	(8,602)	3,713
Comprehensive income (loss) for the period	(199,459)	2,301	(114,509)
Comprehensive income attributable to the noncontrolling interests	(22,504)	(16,543)	(8,824)
Comprehensive loss attributable to MDC Partners Inc.	$ (221,963)	$ (14,242)	$ (123,333)

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current Assets:
Cash and cash equivalents	$ 60,757	$ 106,933
Accounts receivable, less allowance for doubtful accounts of $5,473 and $3,304	374,892	449,288
Expenditures billable to clients	10,552	30,133
Other current assets	40,939	35,613
Total Current Assets	487,140	621,967
Fixed assets, at cost, less accumulated depreciation of $136,166 and $129,579	90,413	81,054
Right-of-use assets - operating leases	214,188	223,622
Goodwill	668,211	731,691
Other intangible assets, net	33,844	54,893
Deferred tax assets	179	84,900
Other assets	17,339	30,179
Total Assets	1,511,314	1,828,306
Current Liabilities:
Accounts payable	168,398	200,148
Accruals and other liabilities	274,968	353,575
Advance billings	112,755	216,931
Current portion of lease liabilities - operating leases	41,208	48,659
Current portion of deferred acquisition consideration	53,730	45,521
Total Current Liabilities	691,260	819,645
Long-term debt	843,184	887,630
Long-term portion of deferred acquisition consideration	29,335	29,699
Long-term lease liabilities - operating leases	247,243	219,163
Other liabilities	82,065	25,771
Total Liabilities	1,893,087	1,981,908
Redeemable Noncontrolling Interests	27,137	36,973
Commitments and Contingencies
Shareholders’ Deficit:
Convertible preference shares, 145,000 authorized, issued and outstanding at December 31, 2020 and 2019	152,746	152,746
Common stock and other paid-in capital	104,367	101,469
Accumulated deficit	(709,751)	(480,779)
Accumulated other comprehensive income (loss)	2,739	(4,269)
MDC Partners Inc. Shareholders' Deficit	(449,899)	(230,833)
Noncontrolling interests	40,989	40,258
Total Shareholders' Deficit	(408,910)	(190,575)
Total Liabilities, Redeemable Noncontrolling Interests and Shareholders' Deficit	1,511,314	1,828,306
Advance Billings [Member]
Current Liabilities:
Advance billings	$ 152,956	$ 171,742

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 3,304	$ 1,879
Fixed assets, accumulated depreciation	$ 129,579	$ 128,546
Preference shares, authorized (in shares)	145,000	95,000
Preference shares, issued (in shares)	145,000	95,000
Preference shares, outstanding (in shares)	145,000	95,000

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (207,197)	$ 10,903	$ (118,222)
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Stock-based compensation	14,179	31,040	18,416
Depreciation and amortization	36,905	38,329	46,196
Impairment and other losses	96,399	8,599	87,204
Adjustment to deferred acquisition consideration	42,187	5,403	(374)
Deferred income taxes (benefits)	108,556	4,791	21,585
(Gain) loss on disposition of assets	771	(4,107)	22,451
Changes in working capital:
Accounts receivable	72,453	(37,763)	31,326
Expenditures billable to clients	19,581	12,236	(11,223)
Prepaid expenses and other current assets	24,840	3,474	(17,189)
Accounts payable, accruals and other current liabilities	(144,123)	(14,077)	(18,222)
Acquisition related payments	(13,330)	(5,223)	(29,141)
Payments For (Proceeds From) Cash In Trust	0	0	(656)
Advance billings	(18,662)	32,934	(14,871)
Net cash provided by operating activities	32,559	86,539	17,280
Cash flows from investing activities:
Capital expenditures	(24,310)	(18,596)	(20,264)
Proceeds from sale of assets	19,616	23,050	2,082
Acquisitions, net of cash acquired	(1,816)	(4,823)	(32,713)
Other	(1,777)	484	464
Net cash provided by (used in) investing activities	(8,287)	115	(50,431)
Cash flows from financing activities:
Proceeds from issuance of common and convertible preference shares, net of issuance costs	0	98,620	0
Acquisition related payments	(35,391)	(30,155)	(32,172)
Distributions to noncontrolling interests and other	(16,036)	(12,049)	(14,537)
Repurchase of Bonds	(21,999)	0	0
Net cash provided by (used in) financing activities	(73,426)	(11,729)	21,434
Effect of exchange rate changes on cash, cash equivalents, and cash held in trusts	2,978	1	77
Cash, Cash Equivalents, Restricted Cash, Restricted Cash Equivalents and Cash Held in Trusts Including Cash Classified Within Assets Held for Sale, Period Increase (Decrease)	(46,176)	74,926	(11,640)
Change in cash and cash equivalents classified within assets held for sale	0	4,441	0
Net increase (decrease) in cash, cash equivalents, and cash held in trusts including cash classified within assets held for sale	(46,176)	76,060	(19,938)
Cash and cash equivalents at beginning of period	106,933	30,873	50,811
Cash and cash equivalents at end of period	60,757	106,933	30,873
Supplemental disclosures:
Cash income taxes paid	7,946	2,296	3,836
Cash interest paid	57,752	62,223	64,012
Wells Fargo Capital Finance, LLC | Revolving Credit Facility
Cash flows from financing activities:
Repayment of borrowings under revolving credit facility	(550,135)	(1,303,350)	(1,625,862)
Proceeds from borrowings under revolving credit facility	550,135	1,235,205	1,694,005
Change in cash and cash equivalents held in trusts classified within held for sale	$ 0	$ (3,307)	$ (8,298)

CONSOLIDATED STATEMENTS OF SHAR

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 (Loss)	MDC Partners Inc. Shareholders' Deficit	Noncontrolling Interests	Common Class ACommon Shares	Series 4 Convertible Preferred StockConvertible Preference Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of adoption of ASC 606	$ (1,170)				$ (1,170)		$ (1,170)
Balance at Dec. 31, 2017	(159,862)	$ 90,220		$ 38,191	(344,349)	$ (1,954)	(217,892)	$ 58,030
Balance (in shares) at Dec. 31, 2017										95,000,000
Common stock, balance (in shares) at Dec. 31, 2017			56,375,131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(130,007)						(130,007)
Other comprehensive income (loss)	3,713					6,674	6,674	(2,961)
Expenses for convertible preference shares	(97)	(97)					(97)
Vesting of restricted stock (in shares)			243,529
Vesting of restricted stock	0
Shares acquired and cancelled	(776)			$ (776)			(776)
Shares acquired and cancelled (in shares)			(108,898)
Shares issued, acquisitions (in shares)				1,011,561
Shares issued, acquisitions	7,030			$ 7,030			7,030
Stock-based compensation	8,165			8,165			8,165
Changes in redemption value of redeemable noncontrolling interests	(4,171)			(4,171)			(4,171)
Business acquisitions and step-up transactions, net of tax	25,550			10,140			10,140	15,410
Changes in ownership interest	(5,965)			0			0	(5,965)
Balance at Dec. 31, 2018	(257,590)	90,123		58,579	(475,526)	4,720	(322,104)	64,514
Balance (in shares) at Dec. 31, 2018										95,000,000
Common stock, balance (in shares) at Dec. 31, 2018			57,521,323
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(5,253)						(5,253)
Other comprehensive income (loss)	(8,602)					(8,989)	(8,989)	387
Issuance of common and convertible preference shares (in shares)			14,285,714							50,000,000
Issuance of common and convertible preference shares	98,620	62,623		35,997			98,620
Vesting of restricted stock (in shares)			576,932
Shares acquired and cancelled	(601)			(601)			(601)
Shares acquired and cancelled (in shares)			(229,366)
Stock-based compensation	3,655			3,655			3,655
Changes in redemption value of redeemable noncontrolling interests	3,160			3,160			3,160
Business acquisitions and step-up transactions, net of tax	1,911			1,911			1,911
Changes in ownership interest	(24,733)			(91)			(91)	(24,642)
Other	(1,142)			(1,141)	0		(1,141)	(1)
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									72,150,854	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.	(228,971)				(228,971)
Other comprehensive income (loss)	7,738					7,008	7,008	730
Vesting of restricted stock (in shares)			1,808,984
Vesting of restricted stock	0
Shares acquired and cancelled	(905)			(905)			(905)
Shares acquired and cancelled (in shares)			(430,739)
Stock-based compensation	6,629			6,629			6,629
Changes in redemption value of redeemable noncontrolling interests	(2,800)			(2,800)			(2,800)
Business acquisitions and step-up transactions, net of tax	1,626			1,626			1,626
Other	(1,652)			(1,652)	(1)		(1,653)	1
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									73,529,105	145,000,000
Common stock, balance (in shares) at Dec. 31, 2020			73,532,848

Basis of Presentation and Recen

Basis of Presentation and Recent Developments	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Recent Developments	Basis of Presentation and Recent Developments The accompanying consolidated financial statements include the accounts of MDC Partners Inc. (the “Company” or “MDC”), its subsidiaries and variable interest entities for which the Company is the primary beneficiary. MDC has prepared the consolidated 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 financial information on Form 10-K. 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 COVID-19 pandemic negatively impacted the Company’s results of operations, financial position, and cash flows in 2020. The Company took actions to address the impact of the pandemic, such as working closely with our clients, reducing our expenses and monitoring liquidity. The impact of the pandemic and the corresponding actions are reflected in our judgments, assumptions and estimates in the preparation of the financial statements. If the duration of the COVID-19 pandemic is longer and the operational impact is greater than estimated, the judgments, assumptions and estimates will be updated and could result in different results in the future. 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. Certain reclassifications have been made to the prior year financial information to conform to the current year presentation. The Company reorganized its management structure in 2020 which resulted in a change to our reportable segments. Prior periods presented have been recast to reflect the change in reportable segments. See Note 20 of the Notes to the Consolidated Financial Statements included herein. Nature of Operations MDC Partners Inc., 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 Company operates in North America, Europe, Asia, South America, and Australia. Recent Developments On December 21, 2020, MDC and Stagwell Media LP, a Delaware limited partnership (“Stagwell”), announced that they 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”). Under the terms of the Transaction Agreement, the combination between MDC and the Stagwell Entities will be effected using an “Up-C” partnership structure. Through a series of steps and transactions (collectively, the “Transactions”), including the domestication of MDC to a Delaware corporation and the merger of MDC Delaware with one of its indirect wholly owned subsidiaries (the “MDC Merger”), MDC Delaware will become a direct subsidiary (from and after the merger, “OpCo”) of a newly-formed, Delaware-organized, NASDAQ-listed corporation (“New MDC”). Following the MDC Merger, (i) OpCo will convert into a limited liability company that will hold MDC’s operating assets and to which Stagwell will contribute the equity interests of the Stagwell Entities (the “Stagwell Contribution”) in exchange for 216,250,000 common membership interests of OpCo (the “Stagwell OpCo Units”), and (ii) Stagwell will contribute to New MDC an aggregate amount of cash equal to $100 in exchange for shares of a new Class C series of voting-only common stock (the “New MDC Class C Stock”) equal in number to the Stagwell OpCo Units. On a pro forma basis, without giving effect to any outstanding preference shares of MDC, the existing holders of MDC’s Class A and Class B shares would receive interests equal to approximately 26% of the combined company and Stagwell would be issued New MDC Class C Stock equivalent to approximately 74% of the voting rights of the combined company and exchangeable, together with Stagwell OpCo Units, into Class A shares of New MDC on a one-for-one basis at Stagwell’s election. The number of Stagwell OpCo Units and shares of New MDC Class C Stock that Stagwell will receive in the Transactions, and the percentage of the combined company that Stagwell will hold following the consummation of the Transactions, will be reduced, and the percentage of the combined company that existing MDC shareholders will hold will be proportionally increased, if Stagwell is unable to effect certain restructuring transactions prior to the closing of the Transactions. On December 21, 2020, MDC and Broad Street Principal Investments, L.L.C., an affiliate of Goldman Sachs (“Broad Street”), entered into a letter agreement, pursuant to which Broad Street consented to the Transactions subject to entry with MDC into a definitive agreement reflecting revised terms of MDC’s issued and outstanding Series 4 convertible preference shares (the “Goldman Letter Agreement”). The revised terms of the Series 4 convertible preference shares would (subject to the closing of the Transactions) reduce the conversion price from $7.42 to $5.00 and extend accretion for two years beyond the date on which accretion would have otherwise ceased, at a reduced rate of 6%. In connection with the closing of the Transactions, Broad Street will have the right to redeem up to $30 million of its preference shares in exchange for a $25 million subordinated note or loan with a 3-year maturity (i.e., exchange at an approximately 17% discount to face value). The $25 million note or loan will accrue interest at 8.0% per annum and is, pre-payable any time at par without penalty. On December 21, 2020, MDC entered into consent and support agreements (the “Consent and Support Agreements”) with holders of more than 50% of the aggregate principal amount of its Senior Notes to consent to the consummation of the combination of MDC with the Stagwell Entities. Pursuant to the Consent and Support Agreements, MDC agreed to increase the interest rate on the Senior Notes by 1% per annum effective as of the date of the Consent and Support Agreements and to pay a consent fee of 2% to all holders of Notes upon a successful consent solicitation, or 3% if a supplemental indenture with the waivers and amendments is executed and becomes operative and the combination of MDC with the Stagwell Entities is consummated. On February 5, 2021, MDC announced it had received and accepted consents from holders of at least a majority in principal amount of the Senior Notes, and on February 8, 2021, MDC entered into a supplemental indenture providing for waivers and amendments in connection with the combination of MDC with the Stagwell Entities. On February 8, 2021, MDC filed a proxy statement/prospectus on Form S-4, which describes the Transaction Agreement, the Transactions, and ancillary agreements related thereto in more detail.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies The Company’s significant accounting policies are summarized as follows: Principles of Consolidation . The accompanying consolidated financial statements include the accounts of MDC Partners Inc. and its domestic and international controlled subsidiaries that are not considered variable interest entities, and variable interest entities for which the Company is the primary beneficiary. Intercompany balances and transactions have been eliminated in consolidation. Use of Estimates . The preparation of the consolidated financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities including goodwill, intangible assets, contingent deferred acquisition consideration, redeemable noncontrolling interests, deferred tax assets, right-of-use assets and the amounts of revenue and expenses reported during the period. These estimates are evaluated on an ongoing basis and are based on historical experience, current conditions and various other assumptions believed to be reasonable under the circumstances. These estimates require the use of assumptions about future performance, which are uncertain at the time of estimation. To the extent actual results differ from the assumptions used, results of operations and cash flows could be materially affected. Fair Value . The Company applies the fair value measurement guidance for financial assets and liabilities that are required to be measured at fair value and for non-financial assets and liabilities that are not required to be measured at fair value on a recurring basis, including goodwill, right-of-use assets and other identifiable intangible assets. See Note 18 of the Notes to the Consolidated Financial Statements included herein for additional information regarding fair value measurements. Concentration of Credit Risk . The Company provides marketing communications services to clients who operate in most industry sectors. Credit is granted to qualified clients in the ordinary course of business. Due to the diversified nature of the Company’s client base, the Company does not believe that it is exposed to a concentration of credit risk. No client accounted for more than 10% of the Company’s consolidated accounts receivable as of December 31, 2020 or December 31, 2019. No sales to an individual client or country other than in the United States accounted for more than 10% of revenue for the fiscal years ended December 31, 2020, 2019, or 2018. As the Company operates in foreign markets, it is always considered at least reasonably possible foreign operations will be disrupted in the near term. Cash and Cash Equivalents . The Company’s cash equivalents are primarily comprised of investments in overnight interest-bearing deposits, money market instruments and other short-term investments with original maturity dates of three months or less at the time of purchase. The Company has a concentration of credit risk in that there are cash deposits in excess of federally insured amounts. Allowance for Doubtful Accounts . Trade receivables are stated at invoiced amounts less allowances for doubtful accounts. The allowances represent estimated uncollectible receivables associated with potential customer defaults usually due to customers’ potential insolvency. The allowances include amounts for certain customers where a risk of default has been specifically identified. The assessment of the likelihood of customer defaults is based on various factors, including the length of time the receivables are past due, historical experience and existing economic conditions. Expenditures Billable to Clients . Expenditures billable to clients consist principally of outside vendor costs incurred on behalf of clients when providing services that have not yet been invoiced to clients. Such amounts are invoiced to clients at various times over the course of the production process. Fixed Assets . Fixed assets are stated at cost, net of accumulated depreciation. Computers, furniture and fixtures are depreciated on a straight-line basis over periods of three to seven years. 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. Repairs and maintenance costs are expensed as incurred. Leases . Effective January 1, 2019, the Company adopted Accounting Standards Codification, Leases (“ASC 842”). As a result, the 2018 fiscal year has not been adjusted and continues to be reported under ASC 840, Leases. 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. All right-of-use lease assets are reviewed for impairment. See Note 10 of the Notes to the Consolidated Financial Statements included herein for further information on leases. Impairment of Long-lived Assets . A long-lived asset or asset group is tested for recoverability whenever events or changes in circumstances indicate that its carrying amount may not be recoverable. When such events occur, the Company compares the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset or asset group to the carrying amount of such asset or asset group. If this comparison indicates that there is an impairment, the amount of the impairment is typically calculated using discounted expected future cash flows where observable fair values are not readily determinable. The discount rate applied to these cash flows is based on the Company’s weighted average cost of capital (“WACC”), risk adjusted where appropriate, or other appropriate discount rate. Equity Method Investments . Equity method investments are investments in entities in which the Company has an ownership interest of less than 50% and has significant influence, or joint control by contractual arrangement, (i) over the operating and financial policies of the affiliate or (ii) has an ownership interest greater than 50%; however, the substantive participating rights of the noncontrolling interest shareholders preclude the Company from exercising unilateral control over the operating and financial policies of the affiliate. The Company ’ s proportionate share of the net income or loss of equity method investments is included in the results of operations and any dividends and distributions reduce the carrying value of the investments. The Company’s equity method investments, include various interests in investment funds. The carrying amount for these investments, which are included in Other assets within the Consolidated Balance Sheets as of December 31, 2020 and 2019 was $3,947 and $6,161, respectively. The Company’s management periodically evaluates these investments to determine if there has been a decline in value that is other than temporary. Other Investments . From time to time, the Company makes investments in start-ups, such as advertising technology and innovative consumer product companies, where the Company does not exercise significant influence over the operating and financial policies of the investee. Non-marketable equity investments do not have a readily determinable fair value and are recorded at cost, less any impairment, adjusted for qualifying observable investment balance changes. The carrying amount for these investments, which are included in Other assets within the Consolidated Balance Sheets as of December 31, 2020 and 2019 was $7,257 and $9,854, respectively. The Company is required to measure these other investments at fair value and recognize any changes in fair value within net income or loss. For investments that don’t have readily determinable fair values, and don’t qualify for certain criteria, an alternative for measurement exists. The alternative is to measure these investments at cost, less any impairment, plus or minus changes resulting from observable price changes in orderly transactions for the identical or a similar investment of the same issuer. The Company has elected to measure these investments under the alternative method. The Company performs a qualitative assessment to review these investments for impairment by identifying any impairment indicators, such as significant deterioration of earnings or significant change in the industry. If the qualitative assessment indicates an investment is impaired, the Company estimates the fair value and reduces the carrying value of the investment down to its fair value with the loss recorded within net income or loss. Goodwill . Goodwill (the excess of the acquisition cost over the fair value of the net assets acquired) acquired as a result of a business combination which is not subject to amortization is tested for impairment, at the reporting unit level, annually as of October 1st of each year, or more frequently if indicators of potential impairment exist. For the annual impairment test, the Company has the option of assessing qualitative factors to determine whether it is more likely than not that the carrying amount of a reporting unit exceeds its fair value or performing a quantitative goodwill impairment test. Qualitative factors considered in the assessment include industry and market considerations, the competitive environment, overall financial performance, changing cost factors such as labor costs, and other factors specific to each reporting unit such as change in management or key personnel. If the Company elects to perform the qualitative assessment and concludes that it is more likely than not that the fair value of the reporting unit is more than its carrying amount, then goodwill is not considered impaired and the quantitative impairment test is not necessary. For reporting units for which the qualitative assessment concludes that it is more likely than not that the fair value of the reporting unit is less than its carrying amount and for reporting units for which the qualitative assessment is not performed, the Company will perform the quantitative impairment test, which compares the fair value of the reporting unit to its carrying amount. If the fair value of the reporting unit exceeds the carrying amount of the net assets assigned to that reporting unit, goodwill is not considered impaired. However, if the fair value of the reporting unit is lower than the carrying amount of the net assets assigned to the reporting unit, an impairment charge is recognized equal to the excess of the carrying amount over the fair value. Determining the fair value of a reporting unit involves the use of significant estimates and assumptions. For the 2020 annual impairment test, the Company used an income approach, which incorporates the use of the discounted cash flow (“DCF”) method. The income approach requires the exercise of significant judgment, including judgment about the amount and timing of expected future cash flows, assumed terminal value and appropriate discount rates. The DCF estimates incorporate expected cash flows that represent a spectrum of the amount and timing of possible cash flows of each reporting unit from a market participant perspective. The expected cash flows are developed from the Company’s long-range planning process using projections of operating results and related cash flows based on assumed long-term growth rates, demand trends and appropriate discount rates based on a reporting unit’s WACC as determined by considering the observable WACC of comparable companies and factors specific to the reporting unit. The terminal value is estimated using a constant growth method which requires an assumption about the expected long-term growth rate. The estimates are based on historical data and experience, industry projections, economic conditions, and the Company’s expectations. See Note 8 of the Notes to the Consolidated Financial Statements included herein for additional information regarding the Company’s impairment test. Definite Lived Intangible Assets . Definite lived intangible assets are subject to amortization over their useful lives. The method of amortization selected reflects the pattern in which the economic benefits of the specific intangible asset is consumed or otherwise used. If that pattern cannot be reliably determined, a straight-line amortization method is used over the estimated useful life. Intangible assets that are subject to amortization are reviewed for potential impairment at least annually or whenever events or circumstances indicate that carrying amounts may not be recoverable. For the 2020 annual impairment test, the Company used an income approach, which incorporates the use of the discounted cash flow (“DCF”) method. See Note 8 of the Notes to the Consolidated Financial Statements included herein for further information. Business Combinations. Business combinations are accounted for using the acquisition method and accordingly, the assets acquired (including identified intangible assets), the liabilities assumed and any noncontrolling interest in the acquired business are recorded at their acquisition date fair values. For each acquisition, the Company undertakes a detailed review to identify other intangible assets and a valuation is performed for all such identified assets. The Company uses several market participant measurements to determine the estimated value. This approach includes consideration of similar and recent transactions, as well as utilizing discounted expected cash flow methodologies. A substantial portion of the intangible assets value that the Company acquires is the specialized know-how of the workforce, which is treated as part of goodwill and is not required to be valued separately. The majority of the value of the identifiable intangible assets acquired is derived from customer relationships, including the related customer contracts, as well as trademarks. Deferred Acquisition Consideration . Most acquisitions include an initial payment at the time of closing and provide for future additional contingent purchase price payments. Contingent purchase price obligations for these transactions are recorded as deferred acquisition consideration liabilities, and are derived from the projected performance of the acquired entity and are based on predetermined formulas. These various contractual valuation formulas may be dependent on future events, such as the growth rate of the earnings of the relevant subsidiary during the contractual period. Contingent purchase price obligations are recorded as deferred acquisition consideration on the balance sheet at the acquisition date fair value and are remeasured at each reporting period. The liability is adjusted quarterly based on changes in current information affecting each subsidiary’s current operating results and the impact this information will have on future results included in the calculation of the estimated liability. In addition, changes in various contractual valuation formulas as well as adjustments to present value impact quarterly adjustments. These adjustments are recorded in the results of operations. Redeemable Noncontrolling Interests . Many of the Company’s acquisitions include contractual arrangements where the noncontrolling shareholders have an option to purchase, or may require the Company to purchase, such noncontrolling shareholders’ incremental ownership interests under certain circumstances. The Company has similar call options under the same contractual terms. The amount of consideration under these contractual arrangements is not a fixed amount, but rather is dependent upon various valuation formulas, such as the average earnings of the relevant subsidiary through the date of exercise or the growth rate of the earnings of the relevant subsidiary during that period. In the event that an incremental purchase may be required by the Company, the amounts are recorded as redeemable noncontrolling interests in mezzanine equity on the Consolidated Balance Sheets at their acquisition date fair value and adjusted for changes to their estimated redemption value through Common stock and other paid-in capital in the Consolidated Balance Sheets (but not less than their initial redemption value), except for foreign currency translation adjustments. These adjustments will not impact the calculation of earnings (loss) per share if the redemption values are less than the estimated fair values. See Note 13 of the Notes to the Consolidated Financial Statements for detail on the impact on the Company’s earnings (loss) per share calculation. Subsidiary and Equity Investment Stock Transactions. Transactions involving the purchase, sale or issuance of stock of a subsidiary where control is maintained are recorded as a reduction in the redeemable noncontrolling interests or noncontrolling interests, as applicable. Any difference between the purchase price and noncontrolling interest is recorded to Common stock and other paid-in capital in the Consolidated Balance Sheets. In circumstances where the purchase of shares of an equity investment results in obtaining control, the existing carrying value of the investment is remeasured to the acquisition date fair value and any gain or loss is recognized in the results of operations. Revenue Recognition . The Company’s 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. See Note 5 of the Notes to the Consolidated Financial Statements included herein for additional information. Cost of Services Sold . Cost of services sold primarily consists of staff costs, and does not include depreciation charges for fixed assets. Interest Expense . The Company uses the effective interest method to amortize deferred financing costs and any original issue premium or discount, if applicable. The Company also uses the straight-line method, which approximates the effective interest method, to amortize the deferred financing costs on the Credit Agreement. Income Taxes. We account for income taxes using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized based on the differences between the financial statement carrying value of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates and laws expected to be in effect when the differences are expected to reverse. The Company records associated interest and penalties as a component of income tax expense.The Company records a valuation allowance against deferred income tax assets when management believes it is more likely than not that some portion or all of the deferred income tax assets will not be realized. Management evaluates on a quarterly basis all available positive and negative evidence considering factors such as the reversal of deferred income tax liabilities, taxable income in eligible carryback years, projected future taxable income, the character of the income tax asset, tax planning strategies, changes in tax laws and other factors. The periodic assessment of the net carrying value of the Company’s deferred tax assets under the applicable accounting rules requires significant management judgment. A change to any of these factors could impact the estimated valuation allowance and income tax expense. Stock-Based Compensation . Under the fair value method, compensation cost is measured at fair value at the date of grant and is expensed over the service period, generally the award’s vesting period. The Company uses its historical volatility derived over the expected term of the award to determine the volatility factor used in determining the fair value of the award. The Company recognizes forfeitures as they occur. Stock-based awards that are settled in cash or equity at the option of the Company are recorded at fair value on the date of grant. The fair value measurement of the compensation cost for these awards is based on using the Black-Scholes option pricing-model or other acceptable method and is recorded in Operating income over the service period, in this case the award’s vesting period. The Company has adopted the straight-line attribution method for determining the compensation cost to be recorded during each accounting period. The Company commences recording compensation expense related to awards that are based on performance conditions under the straight-line attribution method when it is probable that such performance conditions will be met. From time to time, certain acquisitions and step-up transactions include an element of compensation related payments. The Company accounts for those payments as stock-based compensation. Retirement Costs . Several of the Company’s subsidiaries offer employees access to certain defined contribution retirement programs. Under the defined contribution plans, these subsidiaries, in some cases, make annual contributions to participants’ accounts which are subject to vesting. The Company’s contribution expense pursuant to these plans was $8,203, $11,909 and $11,136 for the years ended December 31, 2020, 2019, and 2018, respectively. The Company also has a defined benefit pension plan. See Note 12 of the Notes to the Consolidated Financial Statements included herein for additional information on the defined benefit plan. Income (Loss) per Common Share . Basic income (loss) per common share is based upon the weighted average number of common shares outstanding during each period. Diluted income (loss) per common share is based on the above, in addition, if dilutive, common share equivalents, which include outstanding options, stock appreciation rights, and unvested restricted stock units. In periods of net loss, all potentially issuable common shares are excluded from diluted net loss per common share because they are anti-dilutive. The Company has 145,000 authorized and issued convertible preference shares. The two-class method is applied to calculate basic net income (loss) attributable to MDC Partners Inc. per common share in periods in which shares of convertible preference shares are outstanding, as shares of convertible preference shares are participating securities due to their dividend rights. See Note 15 of the Notes to the Consolidated Financial Statements included herein for additional information. The two-class method is an earnings allocation method under which earnings per share is calculated for common stock considering a participating security’s rights to undistributed earnings as if all such earnings had been distributed during the period. Either the two-class method or the if-converted method is applied to calculate diluted net income per common share, depending on which method results in more dilution. The Company’s participating securities are not included in the computation of net loss per common share in periods of net loss because the convertible preference shareholders have no contractual obligation to participate in losses. Foreign Currency Translation . The functional currency of the Company is the Canadian dollar; however, it has decided to use U.S. dollars as its reporting currency for consolidated reporting purposes. Generally, the Company’s subsidiaries use their local currency as their functional currency. Accordingly, the currency impacts of the translation of the Consolidated Balance Sheets of the Company and its non-U.S. dollar based subsidiaries to U.S. dollar statements are included as cumulative translation adjustments in Accumulated other comprehensive income (loss). Translation of intercompany debt, which is not intended to be repaid, is included in cumulative translation adjustments. Cumulative translation adjustments are not included in net earnings (loss) unless they are actually realized through a sale or upon complete, or substantially complete, liquidation of the Company’s net investment in the foreign operation. Translation of current intercompany balances are included in net earnings (loss). The balance sheets of non-U.S. dollar based subsidiaries are translated at the period end rate. The Consolidated Statements of Operation of the Company and its non-U.S. dollar based subsidiaries are translated at average exchange rates for the period. Gains and losses arising from the Company’s foreign currency transactions are reflected in net earnings. Unrealized gains or losses arising on the translation of certain intercompany foreign currency transactions that are of a long-term nature (that is settlement is not planned or anticipated in the future) are included as cumulative translation adjustments in Accumulated other comprehensive (loss) income.

New Accounting Pronouncements

New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2020
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	New Accounting Pronouncement In December 2019, the FASB issued ASU 2019-12, Income Taxes, to simplify the accounting for income taxes, including amending the rules for performing intra-period tax allocations and calculating income taxes in interim periods, the accounting for transactions that result in a step-up in the tax basis of goodwill, as well as other amendments. ASU 2019-12 is effective January 1, 2021. We do not expect the adoption of ASU 2019-12 will have a material effect on our results of operations and financial position.

Acquisitions and Dispositions

Acquisitions and Dispositions	12 Months Ended
	Dec. 31, 2020
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 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 are 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 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 Consolidated Statement of Operations. Sloane was included within Allison & Partners which is included within the All Other category. 2019 Acquisitions On November 15, 2019, the Company acquired the remaining 35% ownership interest of Laird + Partners it did not own for an aggregate purchase price of $2,389, comprised of a closing cash payment of $1,588 and contingent deferred acquisition payments with an estimated present value at the acquisition date of $801. The contingent deferred payments are based on the financial results of the underlying business from 2018 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $5,045. The difference between the purchase price and the redeemable noncontrolling interest of $2,656 was recorded in common stock and other paid-in capital in the Consolidated Balance Sheets. Effective April 1, 2019, the Company acquired the remaining 35% ownership interest of HPR Partners LLC (Hunter) it did not own for an aggregate purchase price of $10,234, comprised of a closing cash payment of $3,890 and additional contingent deferred acquisition payments with an estimated present value at the acquisition date of $6,344. The contingent deferred payments are based on the financial results of the underlying business from 2018 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $9,486. The difference between the purchase price and the noncontrolling interest of $745 was recorded in common stock and other paid-in capital in the Consolidated Balance Sheets. 2019 Disposition On March 8, 2019, the Company consummated the sale of Kingsdale, an operating segment with operations in Toronto and New York City that provides shareholder advisory services. As consideration for the sale, the Company received cash plus the assumption of certain liabilities totaling approximately $50,000 in the aggregate. The sale resulted in a loss of approximately $3,000, which was included in Other, net within the Consolidated Statement of Operations. 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 retention payments, tied to continued employment, 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 December 31, 2020 and December 31, 2019. December 31, 2020 2019 Beginning balance of contingent payments $ 74,671 $ 82,598 Payments (46,792) (30,719) Redemption value adjustments (1) 44,993 15,451 Additions - acquisitions and step-up transactions 7,703 7,145 Other 2,227 196 Ending balance of contingent payments $ 82,802 $ 74,671 Fixed payments 263 549 $ 83,065 $ 75,220 (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 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 for the twelve months ended December 31, 2020 and 2019: 2020 2019 Loss attributable to fair value adjustments $ 42,187 $ 5,403 Stock-based compensation 2,806 10,048 Redemption value adjustments $ 44,993 $ 15,451

Revenue

Revenue	12 Months Ended
	Dec. 31, 2020
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 on a global basis. 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 twelve months ended December 31, 2020, 2019 and 2018: Twelve Months Ended December 31, Industry Reportable Segment 2020 2019 2018 Food & Beverage All $ 205,939 $ 280,094 $ 313,368 Retail All 148,293 148,851 152,552 Consumer Products All 165,105 167,324 162,524 Communications All 77,443 184,870 178,410 Automotive All 67,339 78,985 88,807 Technology All 181,057 118,169 104,479 Healthcare All 100,727 102,221 127,547 Financials All 91,438 112,351 110,069 Transportation and Travel/Lodging All 44,510 88,958 86,419 Other All 117,160 133,980 150,913 $ 1,199,011 $ 1,415,803 $ 1,475,088 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 twelve months ended December 31, 2020, 2019 and 2018: Twelve Months Ended December 31, Geographic Location Reportable Segment 2020 2019 2018 United States All $ 959,636 $ 1,116,045 $ 1,152,399 Canada All 81,930 105,067 124,001 Other All 157,445 194,691 198,688 $ 1,199,011 $ 1,415,803 $ 1,475,088 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 $49,110 and $65,004 at December 31, 2020 and December 31, 2019, respectively, and are included as a component of Accounts receivable on the Consolidated Balance Sheets. Outside vendor costs incurred on behalf of clients which have yet to be invoiced were $10,552 and $30,133 at December 31, 2020 and December 31, 2019, respectively, and are included on the 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 within Accruals and other liabilities on the Company’s 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 Consolidated Statements of Operations. Advance billings at December 31, 2020 and December 31, 2019 were $152,956 and $171,742, respectively. The decrease in the advance billings balance of $18,786 for the twelve months ended December 31, 2020 was primarily driven by cash payments received or due in advance of satisfying our performance obligations, offset by $152,361 of revenues recognized that were included in the advance billings balances as of December 31, 2019 and reductions due to the incurrence of third-party costs. Contract liabilities classified within Accruals and other liabilities at December 31, 2020 and December 31, 2019 were $112,755 and $216,931, respectively. The decrease in the balance of $104,176 for the twelve months ended December 31, 2020 was primarily driven by cash payments received or due in advance of satisfying our performance obligations, offset by $210,078 of revenues recognized that were included in the balance as of December 31, 2019 and reductions due to the incurrence of third-party costs. Changes in the contract asset and liability balances during the twelve months ended December 31, 2020 and December 31, 2019 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 $6,105 of unsatisfied performance obligations as of December 31, 2020, of which we expect to recognize approximately 92% in 2021, and 8% in 2022.

Income (Loss) Per Common Share

Income (Loss) Per Common Share	12 Months Ended
	Dec. 31, 2020
Earnings Per Share [Abstract]
Loss Per Common Share	Loss) Per Common Share The following table sets forth the computation of basic and diluted loss per common share: Twelve Months Ended December 31, 2020 2019 2018 Numerator: Net loss attributable to MDC Partners Inc. $ (228,971) $ (5,253) $ (130,007) Accretion on convertible preference shares (14,179) (12,304) (8,355) Net loss attributable to MDC Partners Inc. common shareholders $ (243,150) $ (17,557) $ (138,362) Denominator: Basic weighted average number of common shares outstanding 72,862,178 69,132,100 57,218,994 Dilutive effect of equity awards — — — Diluted weighted average number of common shares outstanding 72,862,178 69,132,100 57,218,994 Basic $ (3.34) $ (0.25) $ (2.42) Diluted $ (3.34) $ (0.25) $ (2.42) Anti-dilutive stock awards 5,341,846 5,450,426 1,442,518

Fixed Assets Fixed Assets

Fixed Assets Fixed Assets	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Fixed Assets	Fixed Assets The following is a summary of the Company’s fixed assets as of December 31: 2020 2019 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 93,850 $ (74,766) $ 19,084 $ 93,224 $ (69,687) $ 23,537 Leasehold improvements 132,729 (61,400) 71,329 117,409 (59,892) 57,517 $ 226,579 $ (136,166) $ 90,413 $ 210,633 $ (129,579) $ 81,054 Depreciation expense for the years ended December 31, 2020, 2019, and 2018 was $24,598, $25,133 and $27,111, respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets As of December 31, goodwill was as follows: Goodwill Integrated Networks - Group A Integrated Networks -Group B Media & Data Network All Other Total Balance at December 31, 2018 $ 139,452 $ 267,059 $ 101,768 $ 224,473 $ 732,752 Acquired goodwill — 1,025 — — 1,025 Impairment loss recognized (4,879) — — — (4,879) Transfer of goodwill between segments (1) — (120) 3,612 (3,492) — Foreign currency translation — 423 217 2,153 2,793 Balance at December 31, 2019 $ 134,573 $ 268,387 $ 105,597 $ 223,134 $ 731,691 Acquired goodwill — — — — — Disposition — — — (7,074) (7,074) Impairment loss recognized — (16,137) (5,287) (40,237) (61,661) Transfer of goodwill between segments — 19,696 4,546 (24,242) — Foreign currency translation — 212 538 4,505 5,255 Balance at December 31, 2020 $ 134,573 $ 272,158 $ 105,394 $ 156,086 $ 668,211 (1) Transfers of goodwill relate to changes in segments. For the twelve months ended December 31, 2020, the Company recognized an impairment charge of $61,661 to write-down the carrying value of goodwill in excess of the fair value at four reporting units, one in the Integrated Networks - Group B reportable segment, one in Media & Data Network reportable segment and two within the All Other category. As of December 31, 2020, there were two reporting units with negative net asset carrying value in the Integrated Networks - Group A reportable segment and the All Other category. The goodwill allocated to these reporting units is $14,854 and $5,479, respectively. For the twelve months ended December 31, 2019, the Company recognized an impairment charge of $4,879 to write-down the carrying value of goodwill in excess of the fair value at one reporting unit within the Integrated Networks - Group A. For the twelve months ended December 31, 2018, the Company recognized an impairment of goodwill and other assets of $87,204 primarily to write-down the carrying value of goodwill in excess of the fair value at three reporting units, one in each of the Integrated Networks - Group B reportable segment, the Media & Data Network reportable segment and within the All Other category. The total accumulated goodwill impairment charges as of December 31, 2020 and 2019, were $238,965 and $177,304, respectively. The gross and net amounts of acquired intangible assets other than goodwill as of December 31, Intangible Assets 2020 2019 Trademark (indefinite life) $ — $ 14,600 Customer relationships – gross $ 52,594 $ 58,211 Less accumulated amortization (32,667) (32,671) Customer relationships – net $ 19,927 $ 25,540 Trademarks (definite life) – gross $ 32,711 $ 28,695 Less accumulated amortization (18,794) (13,942) Trademarks (definite life) – net $ 13,917 $ 14,753 Total intangible assets $ 85,305 $ 101,506 Less accumulated amortization (51,461) (46,613) Total intangible assets – net $ 33,844 $ 54,893 During the first quarter of 2020, the Company reassessed its estimate of the useful life of a trademark in the amount of $14,600, acquired as a result of a business combination. The Company revised the useful life to five years from indefinite lived. During the fourth quarter of 2020, the Company recognized an impairment of two trademarks totaling $12,071, equal to the excess carrying value above the fair value for a reporting unit within the Integrated Networks - Group B reportable segment and a reporting unit within the All Other category. The intangible assets impairment is included in Impairment and other losses in the Consolidated Statement of Operations. The weighted average amortization period for customer relationships is eight years and trademarks is nine years. In total, the weighted average amortization period is eight years. Amortization expense related to amortizable intangible assets for the years ended December 31, 2020, 2019, and 2018 was $11,260, $11,828, and $17,290, respectively. The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2021 $ 8,514 2022 8,062 2023 7,711 2024 4,558 Thereafter 4,999

Deferred Acquisition Considerat

Deferred Acquisition Consideration	12 Months Ended
	Dec. 31, 2020
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 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 are 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 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 Consolidated Statement of Operations. Sloane was included within Allison & Partners which is included within the All Other category. 2019 Acquisitions On November 15, 2019, the Company acquired the remaining 35% ownership interest of Laird + Partners it did not own for an aggregate purchase price of $2,389, comprised of a closing cash payment of $1,588 and contingent deferred acquisition payments with an estimated present value at the acquisition date of $801. The contingent deferred payments are based on the financial results of the underlying business from 2018 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $5,045. The difference between the purchase price and the redeemable noncontrolling interest of $2,656 was recorded in common stock and other paid-in capital in the Consolidated Balance Sheets. Effective April 1, 2019, the Company acquired the remaining 35% ownership interest of HPR Partners LLC (Hunter) it did not own for an aggregate purchase price of $10,234, comprised of a closing cash payment of $3,890 and additional contingent deferred acquisition payments with an estimated present value at the acquisition date of $6,344. The contingent deferred payments are based on the financial results of the underlying business from 2018 to 2020 with final payment due in 2021. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $9,486. The difference between the purchase price and the noncontrolling interest of $745 was recorded in common stock and other paid-in capital in the Consolidated Balance Sheets. 2019 Disposition On March 8, 2019, the Company consummated the sale of Kingsdale, an operating segment with operations in Toronto and New York City that provides shareholder advisory services. As consideration for the sale, the Company received cash plus the assumption of certain liabilities totaling approximately $50,000 in the aggregate. The sale resulted in a loss of approximately $3,000, which was included in Other, net within the Consolidated Statement of Operations. 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 retention payments, tied to continued employment, 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 December 31, 2020 and December 31, 2019. December 31, 2020 2019 Beginning balance of contingent payments $ 74,671 $ 82,598 Payments (46,792) (30,719) Redemption value adjustments (1) 44,993 15,451 Additions - acquisitions and step-up transactions 7,703 7,145 Other 2,227 196 Ending balance of contingent payments $ 82,802 $ 74,671 Fixed payments 263 549 $ 83,065 $ 75,220 (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 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 for the twelve months ended December 31, 2020 and 2019: 2020 2019 Loss attributable to fair value adjustments $ 42,187 $ 5,403 Stock-based compensation 2,806 10,048 Redemption value adjustments $ 44,993 $ 15,451

Leases

Leases	12 Months Ended
	Dec. 31, 2020
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 2032. 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 noncancellable 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 Consolidated Statement 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, another 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 on which the variable lease payments are based upon occur. Some of the Company’s leases include options to extend or renew the lease 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 2021 through 2025. 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 December 31, 2020, the Company has entered into three 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 three leases represent an obligation of the Company that is not reflected within the Consolidated Balance Sheet as of December 31, 2020. The aggregate future liability related to these leases is approximately $25,900. 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 twelve months ended December 31: Twelve Months Ended December 31, Twelve Months Ended December 31, 2020 2019 Lease Cost: Operating lease cost $ 71,257 $ 67,044 Variable lease cost 14,640 18,879 Sublease rental income (11,329) (8,965) Total lease cost $ 74,568 $ 76,958 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 70,277 $ 69,735 Right-of-use assets obtained in exchange for operating lease liabilities and other non-cash adjustments $ 45,663 $ 269,801 Weighted average remaining lease term (in years) - Operating leases 7.2 5.3 Weighted average discount rate - Operating leases 10.6 8.6 In the twelve months ended December 31, 2020, the Company recorded a charge of $22,667, of which $9,969 was to reduce the carrying value of its right-of-use lease assets and related leasehold improvements of certain of its agencies within its Integrated Networks - Group A and Integrated Networks - Group B reportable segments and leased space of Corporate. The remaining $12,698 was related to the acceleration of the variable lease expenses associated with the exit of properties in New York as part of the centralization of the Company’s New York real estate portfolio. 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 Consolidated Statement of Operations. In the twelve months ended December 31, 2019, the Company recorded an impairment charge of $3,700 to reduce the carrying value of four of its right-of-use lease assets and related leasehold improvements. Operating lease expense is included in Office and general expenses in the Consolidated Statement of Operations. The Company’s lease expense for leases with a term of 12 months or less is immaterial. Rental expense for the twelve months ended December 31, 2018 was $65,093, offset by $3,671, in sublease rental income. The following table presents minimum future rental payments under the Company’s leases at December 31, 2020 and their reconciliation to the corresponding lease liabilities: Maturity Analysis 2021 $ 68,375 2022 60,252 2023 56,842 2024 49,909 2025 38,880 2026 and thereafter 150,950 Total 425,208 Less: Present value discount (136,757) Lease liability $ 288,451

Debt

Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Debt	Debt As of December 31, 2020 and 2019, the Company’s indebtedness was comprised as follows: December 31, 2020 December 31, 2019 Revolving credit agreement $ — $ — Senior Notes 870,256 900,000 Debt issuance costs (27,072) (12,370) $ 843,184 $ 887,630 Interest expense related to long-term debt for the years ended December 31, 2020, 2019, and 2018 was $59,147, $62,210 and $64,420, respectively. The amortization of debt issuance costs included in interest expense for the years ended December 31, 2020, 2019 and 2018 was $3,529, $3,346 and 3,193, respectively. The revolving credit agreement is a variable rate debt, the carrying value of which approximates fair value. The Company’s Senior Notes are a fixed rate debt instrument recorded at carrying value. 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 exceptions 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. In April 2020, the Company repurchased $29,744 of the Senior Notes, at a weighted average price equal to 73.9% of the principal amount totaling $21,999, and accrued interest of $946. As a result of the repurchase, we recognized an extinguishment gain of $7,388. In connection with the Consent and Support Agreements, beginning December 21, 2020, the Company began to accrue interest at a rate of 7.50% and accrued $17.4 million for the 2% consent fees. The consent fees were capitalized as an offset to the carrying value of the Senior Notes and will be recognized through interest expense over the remaining maturity term of the Senior Notes. 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 December 31, 2020. Revolving Credit Agreement The Company is party to a $211,500 secured revolving credit facility due February 3, 2022. The Company had no amounts outstanding under the revolving credit facility as of December 31, 2020 and December 31, 2019. On May 29, 2020, the Company, Maxxcom Inc., a subsidiary of the Company (“Maxxcom”), and each of their subsidiaries party thereto entered into an amendment (the “Second Amendment”) to the existing senior secured revolving credit facility, dated as of May 3, 2016 (as amended, the “Credit Agreement”), among the Company, Maxxcom, each of their subsidiaries party thereto, Wells Fargo Capital Finance, LLC, as agent (“Wells Fargo”), and the lenders from time to time party thereto. Advances under the Credit Agreement are to be used for working capital and general corporate purposes, in each case pursuant to the terms of the Credit Agreement. The Second Amendment reduced the aggregate maximum amount of revolving commitments provided by the lenders to $211,500 from $250,000, extended the maturity date of the Credit Agreement from May 3, 2021 to February 3, 2022, and expanded the eligibility criteria for certain of the Company’s receivables to be included in the borrowing base. Advances under the Credit Agreement, as amended by the Second Amendment, will 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 Second Amendment increased the required minimum earnings before interest, taxes and depreciation and amortization from $105,000 to $120,000 measured on a trailing 12-month basis. The total leverage ratio applicable on each testing date through the period ending December 31, 2020 remained at 6.25:1.0. The total leverage ratio applicable on each testing date after December 31, 2020 will be 5.5:1.0. 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 December 31, 2020. At December 31, 2020 and December 31, 2019, the Company had issued undrawn outstanding letters of credit of $18,651 and $4,836, respectively. Future Principal Repayments Future principal repayments on the Senior Notes in the aggregate principal amount of $870,256 are due in 2024.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Benefit Plans	Employee Benefit Plans A subsidiary of the Company, sponsors a defined benefit plan with benefits based on each employee’s years of service and compensation. The benefits under the defined benefit pension plan are frozen. Net Periodic Pension Cost and Pension Benefit Obligation Net periodic pension cost consists of the following components for the years ended December 31: Pension Benefits 2020 2019 2018 Service cost $ — $ — $ — Interest cost on benefit obligation 1,426 1,640 1,641 Expected return on plan assets (1,924) (1,604) (1,948) Curtailment and settlements 2,333 626 1,039 Amortization of actuarial (gains) losses 340 266 258 Net periodic benefit cost $ 2,175 $ 928 $ 990 The above costs are included within Other, net on the Consolidated Statements of Operations. The following weighted average assumptions were used to determine net periodic costs at December 31: Pension Benefits 2020 2019 2018 Discount rate 3.39 % 4.42 % 3.83 % Expected return on plan assets 7.00 % 7.00 % 7.00 % Rate of compensation increase N/A N/A N/A The expected return on plan assets is a long-term assumption established by considering historical and anticipated returns of the asset classes invested in by the pension plan and the allocation strategy currently in place among those classes. Other changes in plan assets and benefit obligation recognized in Other comprehensive income (loss) consist of the following components for the years ended December 31: Pension Benefits 2020 2019 2018 Current year actuarial (gain) loss $ 2,213 $ 2,917 $ (520) Amortization of actuarial loss (340) (266) (258) Total recognized in other comprehensive (income) loss 1,873 2,651 (778) Total recognized in net periodic benefit cost and other comprehensive loss $ 4,048 $ 3,579 $ 212 The following table summarizes the change in benefit obligations and fair values of plan assets for the years ended December 31: 2020 2019 2018 Change in benefit obligation: Benefit obligation, Beginning balance $ 43,012 $ 37,938 $ 43,750 Interest Cost 1,426 1,640 1,641 Actuarial (gains) losses 5,301 6,127 (3,522) Benefits paid (6,728) (2,693) (3,931) Benefit obligation, Ending balance 43,011 43,012 37,938 Change in plan assets: Fair value of plan assets, Beginning balance 27,206 23,181 27,977 Actual return on plan assets 2,678 4,188 (2,093) Employer contributions 2,325 2,530 1,228 Benefits paid (6,728) (2,693) (3,931) Fair value of plan assets, Ending balance 25,481 27,206 23,181 Unfunded status $ 17,530 $ 15,806 $ 14,757 Amounts recognized in the balance sheet at December 31 consist of the following: Pension Benefits 2020 2019 Non-current liability $ 17,530 $ 15,806 Net amount recognized $ 17,530 $ 15,806 Amounts recognized in Accumulated Other Comprehensive Loss before income taxes consists of the following components for the years ended December 31: Pension Benefits 2020 2019 Accumulated net actuarial losses $ 17,403 $ 15,530 Amount recognized $ 17,403 $ 15,530 In 2021, the Company estimates that it will recognize $413 of amortization of net actuarial losses from accumulated other comprehensive loss, net into net periodic cost related to the pension plan. The following weighted average assumptions were used to determine benefit obligations as of December 31: Pension Benefits 2020 2019 Discount rate 2.55 % 3.39 % Rate of compensation increase N/A N/A The discount rate assumptions at December 31, 2020 and 2019 were determined independently. The discount rate was derived from the effective interest rate of a hypothetical portfolio of high-quality bonds, whose cash flows match the expected future benefit payments from the plan as of the measurement date. Fair Value of Plan Assets and Investment Strategy The fair value of the plan assets as of December 31, is as follows: December 31, 2020 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,039 $ 1,039 $ — $ — Mutual funds 24,442 24,442 — — Total $ 25,481 $ 25,481 $ — $ — December 31, 2019 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,275 $ 1,275 $ — $ — Mutual funds 25,931 25,931 — — Total $ 27,206 $ 27,206 $ — $ — The pension plans weighted-average asset allocation for the years ended December 31, 2020 and 2019 are as follows: Target Allocation Actual Allocation 2020 2020 2019 Asset Category: Equity securities 65.0 % 69.0 % 66.7 % Debt securities 30.0 % 27.0 % 28.6 % Cash/cash equivalents and Short term investments 5.0 % 4.0 % 4.7 % 100.0 % 100.0 % 100.0 % The goals of the pension plan investment program are to fully fund the obligation to pay retirement benefits in accordance with the plan documents and to provide returns that, along with appropriate funding from the Company, maintain an asset/liability ratio that is in compliance with all applicable laws and regulations and assures timely payment of retirement benefits. Equity securities primarily include investments in large-cap and mid-cap companies located in the United States. Debt securities are diversified across different asset types with bonds issued in the United States as well as outside the United States. Investment securities are exposed to various risks such as interest rate, market, and credit risks. Due to the level of risk associated with certain investment securities, it is at least reasonably possible that changes in the values of investment securities will occur in the near term and that such changes could materially affect the amounts reported in the preceding tables. Cash Flows The pension plan contributions are deposited into a trust, and the pension plan benefit payments are made from trust assets. During 2020, the Company contributed $2,325 to the pension plan. The Company estimates that it will make approximately $2,415 in contributions to the pension plan in 2021. Fluctuations in actual market returns as well as changes in general interest rates will result in changes in the market value of plan assets and may result in increased or decreased retirement benefit costs and contributions in future periods. The following estimated benefit payments, which reflect expected future service, as appropriate, are expected to be paid in the years ending December 31: Period Amount 2021 $ 1,802 2022 1,769 2023 1,983 2024 2,231 2025 2,171 Thereafter 10,796

Noncontrolling and Redeemable N

Noncontrolling and Redeemable Noncontrolling Interests	12 Months Ended
	Dec. 31, 2020
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 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 common stock and other 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 Consolidated Balance Sheets. Noncontrolling Interests Changes in amounts due to noncontrolling interest holders included in Accruals and other liabilities on the Consolidated Balance Sheets for the twelve months ended December 31, 2020 and 2019 were as follows: Noncontrolling Balance, December 31, 2018 $ 9,278 Income attributable to noncontrolling interests 16,156 Distributions made (11,392) Other (14) Balance, December 31, 2019 $ 14,028 Income attributable to noncontrolling interests 21,774 Distributions made (15,192) Other 94 Balance, December 31, 2020 $ 20,704 Changes in the Company’s ownership interests in our less than 100% owned subsidiaries during the three years ended December 31, were as follows: Years Ended December 31, 2020 2019 2018 Net loss attributable to MDC Partners Inc. $ (228,971) $ (5,253) $ (130,007) Transfers from the noncontrolling interest: Increase in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests 1,626 1,911 10,140 Net transfers from noncontrolling interests $ 1,626 $ 1,911 $ 10,140 Change from net loss attributable to MDC Partners Inc. and transfers to noncontrolling interests $ (227,345) $ (3,342) $ (119,867) Redeemable Noncontrolling Interests The following table presents changes in redeemable noncontrolling interests as of December 31, 2020 and 2019: Years Ended December 31, 2020 2019 Beginning Balance $ 36,973 $ 51,546 Redemptions (12,289) (14,530) Granted — — Changes in redemption value 2,800 (3,163) Currency translation adjustments (347) 3 Other — 3,117 Ending Balance $ 27,137 $ 36,973 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 $27,137 as of December 31, 2020, consists of $17,184 assuming that the subsidiaries perform over the relevant future periods at their discounted cash flows earnings level and such rights are exercised, $9,953 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	12 Months Ended
	Dec. 31, 2020
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. Significant judgment is required to determine both likelihood of there being and the estimated amount of a loss related to such matters. Additionally, 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 9 and 13 of the Notes to the 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 twelve months ended December 31, 2020, 2019, and 2018 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 December 31, 2020, the Company had $18,651 of undrawn letters of credit. The Company entered into operating leases for which the commencement date has not yet occurred as of December 31, 2020. See Note 10 of the Notes to the Consolidated Financial Statements included herein for additional information.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2020
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 twelve months ended December 31, 2020 and 2019, the Series 6 Preference Shares accreted at a monthly rate of $7.54 and $6.96 per Series 6 Preference Share, for total accretion of $4,390 and $3,261, respectively, bringing the aggregate liquidation preference to $57,651 as of December 31, 2020. The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. 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. See Note 1 of the Notes to the Consolidated Financial Statements for information regarding revised terms of the Series 4 Preference Shares subject to closing of the combination between MDC and the Stagwell Entities. 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 twelve months ended December 31, 2020 and 2019, the Series 4 Preference Shares accreted at a monthly rate of approximately $8.84 and $8.17 per Series 4 Preference Share, for total accretion of $9,789 and $9,043, respectively, bringing the aggregate liquidation preference to $128,539 as of December 31, 2020. The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. 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 73,529,105 and 72,150,854 Class A Shares issued and outstanding as of December 31, 2020 and 2019, 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 3,749 Class B Shares issued and outstanding as of December 31, 2020 and 2019, respectively. Shares-based Awards As of December 31, 2020, a total of 18,150,000 shares have been authorized under our employee stock incentive plans, of which 5,108,583 remain available to be issued for future awards. The following tables summarize share-based activity of awards authorized under our employee stock incentive plans and awards (such as inducement awards) and other share-based commitments that have met the requirements to be issued separate from shareholder-approved stock incentive plans. The following table summarizes information about financial performance based and time based restricted stock and restricted stock unit awards: Performance-Based Awards Time-Based Awards Shares Weighted Average Grant Date Fair Shares Weighted Average Balance at December 31, 2019 2,443,801 $ 3.11 568,960 $ 5.53 Granted 685,369 2.19 1,741,280 1.97 Vested (555,226) 2.96 (1,031,159) 3.39 Forfeited (336,950) 3.07 (141,821) 3.32 Balance at December 31, 2020 2,236,994 $ 3.37 1,137,260 $ 2.29 Performance based and time-based awards granted in the twelve months ended December 31, 2019 had a weighted average grant date fair value of $3.08 and $2.54, respectively. Performance based and time-based awards granted in December 31, 2018 had a weighted average grant date fair value of $9.17 and $7.38, respectively. The vesting of the performance-based awards is contingent upon the Company meeting cumulative earnings targets over one to three years and continued employment through the vesting date. The term of the time-based awards is generally three years with vesting up to generally three years. The vesting period of the time-based and performance awards is generally commensurate with the requisite service period. The total fair value of restricted stock and restricted stock unit awards, which vested during the years ended December 31, 2020, 2019 and 2018 was $5,138, $4,517 and $3,583, respectively. At December 31, 2020, the weighted average remaining contractual life for time based and performance-based awards was 1.07 and 1.82 years, respectively. At December 31, 2020, the unrecognized compensation expense for performance-based awards was $3,976 to be recognized over a weighted average period of 1.82 years. At December 31, 2020, the unrecognized compensation expense for time-based awards was $570 to be recognized over a weighted average period of 1.07 years. The following table summarizes information about share option awards: Share Option Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2019 111,866 $ 2.23 $ 4.85 Granted — — — Forfeited (111,866) 2.23 4.85 Exercised — — — Balance at December 31, 2020 — $ — $ — We use the Black-Scholes option-pricing model to estimate the fair value of options granted. No options were granted in 2020 and 2019. The grant date fair value of the options granted in 2018 was determined to be $2.23. The assumptions for the model were as follows: expected life of 4.9 years, risk free interest rate of 2.9%, expected volatility of 52.9% and dividend yield of 0%. Options granted in 2018 vest in 3 years. The term of these awards is 5 years. The vesting period of these awards is generally commensurate with the requisite service period. These awards were all forfeited in 2020. No options were exercised during 2020, 2019 and 2018. There are no options outstanding as of December 31, 2020. No options vested in 2020, 2019 and 2018. The following table summarizes information about stock appreciation rights (“SAR”) awards: SAR Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2019 2,325,800 $ 1.14 $ 3.07 Granted — — — Forfeited (250,000) 0.73 5.00 Exercised — — — Balance at December 31, 2020 2,075,800 $ 1.19 $ 2.84 We use the Black-Scholes option-pricing model to estimate the fair value of the SAR awards. No SAR awards were granted in 2020. SAR awards granted in 2019 vest in equal installments on each of the first 3 anniversaries of the grant date and have grant date fair values ranging from $0.68 to $1.41. The assumptions for the model were as follows: expected life of 3 to 4 years, risk free interest rate of 1.8% to 2.3%, expected volatility of 62.5% to 67.1% and dividend yield of 0%. The term of these awards is 5 years. The vesting period of awards granted is generally commensurate with the requisite service period. No SAR awards were granted in 2018. As of December 31, 2020, 775,800 SAR awards vested and were exercisable. The aggregate intrinsic value of the SAR awards outstanding as of December 31, 2020 is $480. No SAR awards were exercised during 2020, 2019 and 2018. No SAR awards vested in 2019 and 2018. At December 31, 2020, the weighted average remaining contractual life for the SAR awards was 0.8 years. At December 31, 2020, the unrecognized compensation expense for these awards was $402 to be recognized over a weighted average period of 0.8 years.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes in Accumulated Other Comprehensive Income (Loss)	Changes in Accumulated Other Comprehensive Income (Loss) The changes in accumulated other comprehensive income (loss) for the twelve months ended December 31 were: Defined Foreign Currency Translation Total Balance December 31, 2018 $ (13,101) $ 17,821 $ 4,720 Other comprehensive income before reclassifications — (7,078) (7,078) Amounts reclassified from accumulated other comprehensive loss (net of tax benefit of $740) (1,911) — (1,911) Other comprehensive income (1,911) (7,078) (8,989) Balance December 31, 2019 $ (15,012) $ 10,743 $ (4,269) Other comprehensive loss before reclassifications — 8,362 8,362 Amounts reclassified from accumulated other comprehensive loss (net of tax benefit of $519) (1,354) — (1,354) Other comprehensive loss (1,354) 8,362 7,008 Balance December 31, 2020 $ (16,366) $ 19,105 $ 2,739

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On March 27, 2020, the Coronavirus Aid, Relief and Economic Security (“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 components of the Company’s income (loss) before income taxes and equity in earnings of non-consolidated affiliates by taxing jurisdiction for the years ended December 31, were: 2020 2019 2018 Income (Loss): U.S. $ (73,227) $ (17,491) $ (76,960) Non-U.S. (15,175) 38,358 (11,709) $ (88,402) $ 20,867 $ (88,669) The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2020 2019 2018 Current tax provision U.S. federal $ 3,016 $ 2,638 $ 444 U.S. state and local 742 12 2 Non-U.S. 4,241 2,875 7,584 7,999 5,525 8,030 Deferred tax provision (benefit): U.S. federal 75,686 4,635 (10,817) U.S. state and local 34,404 1,130 (3,476) Non-U.S. (1,534) (974) 35,878 108,556 4,791 21,585 Income tax expense (benefit) $ 116,555 $ 10,316 $ 29,615 A reconciliation of income tax expense (benefit) using the U.S. federal income tax rate compared with actual income tax expense for the years ended December 31, is as follows: 2020 2019 2018 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ (88,402) $ 20,867 $ (88,669) Statutory income tax rate 21.0 % 21.0 % 21.0 % Tax expense (benefit) using U.S. statutory income tax rate (18,564) 4,382 (18,621) State and foreign taxes (3,486) 1,496 (3,944) Non-deductible stock-based compensation 1,162 3,823 1,512 Global intangible low-taxed income 1,363 1,147 710 Base erosion and anti-abuse tax 4,697 2,504 389 Other non-deductible expense 1,043 273 1,388 Change to valuation allowance 128,938 (2,830) 49,482 Effect of the difference in U.S. federal and local statutory rates 67 1,422 (152) Noncontrolling interests (4,649) (3,566) (2,674) Other impacts of foreign operations 1,160 2,724 612 Impact of goodwill impairments 10,158 436 8,703 Adjustments to accrued taxes in previous periods 4,641 (3,544) 1,192 Adjustment to deferred tax balances* (9,999) 1,920 (8,845) Other, net 24 129 (137) Income tax expense (benefit) $116,555 $10,316 $29,615 Effective income tax rate (131.8)% 49.4% (33.4)% *Adjustments to deferred tax balances in 2020 are primarily offset by changes to valuation allowance. Income tax expense for the twelve months ended December 31, 2020 was $116,555 (associated with a pre-tax loss of $88,402) compared to an income tax expense of $10,316 (associated with pre-tax income of $20,867) for the twelve months ended December 31, 2019. Income tax expense in 2020 included the impact of increasing valuation allowance primarily associated with U.S. deferred tax assets and the impact of non-deductible goodwill impairments of foreign operations. Income tax expense in 2019 included the impact of base erosion and anti-abuse tax and non-deductible stock compensation offset by a reduction in valuation allowance primarily associated with Canadian deferred tax assets. Income taxes receivable were $1,480 and $5,025 at December 31, 2020 and 2019, respectively, and were included in other current assets on the balance sheet. Income taxes payable were $9,238 and $11,722 at December 31, 2020 and 2019, respectively, and were included in accrued and other liabilities on the balance sheet. It is the Company’s policy to classify interest and penalties arising in connection with unrecognized tax benefits as a component of income tax expense. The tax effects of significant temporary differences representing deferred tax assets and liabilities at December 31, were as follows: 2020 2019 Deferred tax assets: Accounting reserves and other $ 20,831 $ 10,987 Net operating loss carryforwards 47,139 60,705 Interest deductions 20,819 16,797 Refinancing charge — 669 Goodwill and intangibles 122,045 117,421 Stock compensation 1,693 1,736 Pension plan 4,856 4,414 Unrealized foreign exchange 11,995 11,373 Capital loss carryforwards 13,657 13,081 Lease liabilities 77,870 76,397 Gross deferred tax asset 320,905 313,580 Less: valuation allowance (198,452) (65,649) Net deferred tax assets 122,453 247,931 Deferred tax liabilities: Right-of-use assets $ (57,890) $ (67,613) Refinancing charge (1,675) — Withholding taxes (475) (546) Capital assets (1,893) (382) Goodwill amortization (88,326) (98,677) Total deferred tax liabilities (150,259) (167,218) Net deferred tax asset (liability) $ (27,806) $ 80,713 Deferred tax assets $ 179 $ 84,900 Deferred tax liabilities (27,985) (4,187) $ (27,806) $ 80,713 The Company has net operating loss carryforwards of $229,224 which expire in years 2021 through 2040. These definite lived net operating loss carryforwards consist of $1,533 relating to U.S. federal, $132,655 relating to U.S. states, and $95,036 relating to non-U.S. The Company also has indefinite net operating loss carryforwards of $122,299. These indefinite loss carryforwards consist of $42,003 relating to the U.S. federal, $69,967 relating to U.S. states, and $10,329 relating to non-U.S. In addition, the Company has indefinite capital loss carryforwards of $103,074 in Canada and foreign tax credit carryforwards in the U.S. of $5,460 which expire in years 2024 through 2027. The Company maintained a valuation allowance of $198,452 as of December 31, 2020 relating to both U.S. and foreign deferred tax assets, and $65,649 as of December 31, 2019 relating to foreign deferred tax assets. The Company records a valuation allowance against deferred income tax assets when management believes it is more likely than not that some portion or all of the deferred income tax assets will not be realized. Management evaluates all positive and negative evidence and considers factors such as the reversal of taxable temporary differences, taxable income in eligible carryback years, future taxable income, and tax planning strategies. A change to these factors could impact the estimated valuation allowance and income tax expense. In 2020, the Company’s evaluation resulted in the recognition of a valuation allowance against its U.S. deferred tax assets. Given a three-year U.S. cumulative pre-tax loss as of December 31, 2020 and other factors, the Company concluded it is more likely than not that such U.S. deferred tax assets will not be realized. Income tax expense for the year ended December 31, 2020 included a charge of approximately $129 million in connection with the change in the valuation allowance, which primarily relates to the U.S. The Company has historically asserted that its unremitted foreign earnings are permanently reinvested except for certain international entities. The Company has provided $475 and $546 as an estimate of the tax costs of repatriation with respect to $4,745 and $5,462 of undistributed foreign earnings from certain international entities that are not subject to the permanent reinvestment assertion as of December 31, 2020 and 2019. We have not changed our permanent reinvestment assertion with respect to any other international entities as we intend to use the related historical earnings and profits to fund international operations and investments, and therefore have not recorded income taxes on such amounts. As of December 31, 2020 and 2019, the Company recorded a liability for unrecognized tax benefits as well as applicable penalties and interest in the amount of $1,066 and $1,107, respectively. As of December 31, 2020 and 2019, accrued penalties and interest included in unrecognized tax benefits were approximately $135 and $111, respectively. If these unrecognized tax benefits were to be recognized, it would affect the Company’s effective tax rate. 2020 2019 2018 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 996 $ 887 $ 1,433 Current year positions 581 275 — Prior period positions — — 7 Settlements — — (314) Lapse of statute of limitations (170) (166) (239) Unrecognized tax benefits - Ending Balance $ 1,407 $ 996 $ 887 The Company has presented $477 of the unrecognized tax benefits as of December 31, 2020 as a reduction to the deferred tax asset. It is reasonably possible that the amount of unrecognized tax benefits could decrease by a range of $400 to $500 in the next twelve months as a result of expiration of certain statute of limitations. The Company is subject to taxation and files income tax returns in the U.S. federal jurisdiction and in many state and foreign jurisdictions. The statute of limitations for tax years prior to 2017 are closed for U.S. federal purposes. The statute of limitations for tax years prior to 2010 have also expired in non-U.S. jurisdictions.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
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 December 31, 2020 and 2019: December 31, 2020 December 31, 2019 Carrying Fair Value Carrying Fair Value Liabilities: Senior Notes $ 870,256 $ 883,580 $ 900,000 $ 812,250 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. Non-financial Assets and Liabilities that are not Measured at Fair Value on a Recurring Basis Certain non-financial assets are measured at fair value on a nonrecurring basis, primarily goodwill, intangible assets (Level 3 fair value assessment) and right-of-use lease assets (Level 2 fair value assessment). 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 recognized an impairment of goodwill of $61,661 for the twelve months ended December 31, 2020 as compared to an impairment of goodwill of $4,879 for the twelve months ended December 31, 2019. The Company also recognized an impairment of intangible assets of $12,071 for the twelve months ended December 31, 2020. See Notes 2 and 8 of the Notes to the Consolidated Financial Statements for information related to the measurement of the fair value of goodwill. In the twelve months ended December 31, 2020, the Company recorded a charge of $22,667, of which $9,969 was to reduce the carrying value of right-of-use lease assets and related leasehold improvements. The remaining $12,698 was related to the acceleration of the variable lease expenses associated with the exit of properties in New York as part of the centralization of the Company’s New York real estate portfolio. 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 December 31, 2020, 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 Consolidated Balance Sheets are subject to material uncertainty. See Note 9 of the Notes to the Consolidated Financial Statements included herein for additional information regarding contingent deferred acquisition consideration.

Related Party Transactions (Not

Related Party Transactions (Notes)	12 Months Ended
	Dec. 31, 2020
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 will collaborate 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 as of December 2020. As of December 31, 2020, $1,200 was owed to the affiliate. During 2020, a Partner Firm of the Company entered into an arrangement with certain Stagwell affiliates to perform media planning, buying and reporting services. Under the arrangement, the Partner Firm is expected to receive from the Stagwell affiliates approximately $56,700, which has been fully recognized as of December 2020. As of December 31, 2020, $110 was due from the affiliates. In January 2020, a Partner Firm of the Company entered into an arrangement with a Stagwell affiliate to develop advertising technology for the Partner Firm. Under the arrangement the Partner Firm recorded approximately $483, of which $2 was owed to the affiliate as of December 31, 2020. This transaction has been completed. In August 2020, the Company entered into an arrangement with a Stagwell affiliate to provide audience and brand research, concept testing and landscape related to the ongoing new business pitches for clients of the Company. Under the arrangement the Company is expected to pay the Stagwell affiliate approximately $145, which has been fully recognized as of October 2020. As of December 31, 2020, $63 was owed to 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 $457, which is expected to be recognized through March of 2021. As of December 31, 2020, $67 was due from the affiliate. On February 14, 2020, Sloane sold substantially all its assets and certain liabilities to an affiliate of Stagwell. See Note 4 of the Notes to the Consolidated Financial Statements for information related to this transaction.

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2020
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 adjustments to Operating income (loss), plus depreciation and amortization, stock-based compensation, deferred acquisition consideration adjustments, distributions from non-consolidated affiliates and other items. 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 severance expense 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. Effective in the first quarter of 2020, the Company reorganized its management structure resulting in the aggregation of certain Partner Firms into integrated groups (“Networks”). Mr. Penn appointed key agency executives, that report directly into him to lead each Network. In connection with the reorganization, we reassessed our reportable segments to align our external reporting with how we operate the Networks under our new organizational structure. Prior periods presented have been recast to reflect the change in reportable segments. The three reportable segments that resulted from our reassessment 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 in Note 2 of the Notes to the Consolidated Financial Statements included herein. • 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. • 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. Years Ended December 31, 2020 2019 2018 Revenue: Integrated Networks - Group A $ 379,648 $ 392,101 $ 393,890 Integrated Networks - Group B 435,589 531,717 551,317 Media & Data Network 139,015 161,451 183,287 All Other 244,759 330,534 346,594 Total $ 1,199,011 $ 1,415,803 $ 1,475,088 Adjusted EBITDA: Integrated Networks - Group A $ 79,793 $ 74,822 $ 75,609 Integrated Networks - Group B 84,297 84,568 74,091 Media & Data Network 9,707 7,746 12,205 All Other 30,755 37,618 38,307 Corporate (27,220) (30,601) (38,761) Total Adjusted EBITDA $ 177,332 $ 174,153 $ 161,451 Depreciation and amortization $ (36,905) $ (38,329) $ (46,196) Impairment and other losses (96,399) (8,599) (87,204) Stock compensation expense (14,179) (31,040) (18,416) Deferred acquisition consideration expense/(income) (42,187) (5,403) 457 Loss on investments (2,175) (2,048) (779) Other expense (31,244) (9,274) (7,879) Total Operating Income (Loss) $ (45,757) $ 79,460 $ 1,434 Other Income (Expenses): Interest expense and finance charges, net $ (62,163) $ (64,942) $ (67,075) Foreign exchange gain (loss) (982) 8,750 (23,258) Other, net 20,500 (2,401) 230 Income (loss) before income taxes and equity in earnings of non-consolidated affiliates (88,402) 20,867 (88,669) Income tax expense 116,555 10,316 29,615 Income (loss) before equity in earnings of non-consolidated affiliates (204,957) 10,551 (118,284) Equity in earnings of non-consolidated affiliates (2,240) 352 62 Net income (loss) (207,197) 10,903 (118,222) Net income attributable to the noncontrolling interest (21,774) (16,156) (11,785) Net loss attributable to MDC Partners Inc. (228,971) (5,253) (130,007) Accretion on and net income allocated to convertible preference shares (14,179) (12,304) (8,355) Net loss attributable to MDC Partners Inc. common shareholders $ (243,150) $ (17,557) $ (138,362) Years Ended December 31, 2020 2019 2018 Depreciation and amortization: (Dollars in Thousands) Integrated Networks - Group A $ 6,467 $ 8,559 $ 9,602 Integrated Networks - Group B 17,204 15,904 19,032 Media & Data Network 4,376 4,303 3,820 All Other 7,478 8,695 12,980 Corporate 1,380 868 762 Total $ 36,905 $ 38,329 $ 46,196 Stock-based compensation: Integrated Networks - Group A $ 7,580 $ 24,420 $ 5,792 Integrated Networks - Group B 3,191 4,303 6,890 Media & Data Network 122 63 320 All Other 304 374 755 Corporate 2,982 1,880 4,659 Total $ 14,179 $ 31,040 $ 18,416 Capital expenditures: Integrated Networks - Group A $ 1,087 $ 5,934 $ 8,228 Integrated Networks - Group B 987 9,270 6,352 Media & Data Network 569 627 1,632 All Other 966 2,729 3,985 Corporate 33,694 36 67 Total $ 37,303 $ 18,596 $ 20,264 A summary of the Company’s long-lived assets, comprised of fixed assets, goodwill and intangibles, net, by geographic region at December 31, is set forth in the following table. United States Canada Other Total Long-lived Assets 2020 $ 80,447 $ 3,461 $ 6,505 $ 90,413 2019 $ 68,497 $ 4,475 $ 8,082 $ 81,054 Goodwill and Intangible Assets 2020 $ 614,168 $ 51,267 $ 36,620 $ 702,055 2019 $ 659,584 $ 64,842 $ 62,158 $ 786,584 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. Corporate’s capital expenditures in 2020 are primarily for leasehold improvements at its new headquarters at One World Trade Center in connection with the centralization of the Company’s New York real estate portfolio. As of December 31, 2020, the Company had $12,993 of capital expenditures that were incurred in the current year, but not yet paid. A summary of the Company’s revenue by geographic region at December 31 is set forth in the following table. United States Canada Other Total Revenue: 2020 $ 959,636 $ 81,930 $ 157,445 $ 1,199,011 2019 $ 1,116,045 $ 105,067 $ 194,691 $ 1,415,803 2018 $ 1,152,399 $ 124,001 $ 198,688 $ 1,475,088

Quarterly Results of Operations

Quarterly Results of Operations	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	Quarterly Results of Operations (Unaudited) The following table sets forth a summary of the Company’s consolidated unaudited quarterly results of operations for the years ended December 31, in thousands of dollars, except per share amounts. Quarters First Second Third Fourth Revenue: 2020 $ 327,742 $ 259,678 $ 283,423 $ 328,168 2019 $ 328,791 $ 362,130 $ 342,907 $ 381,975 Cost of services sold: 2020 $ 222,693 $ 165,632 $ 172,531 $ 209,043 2019 $ 237,154 $ 240,749 $ 222,448 $ 260,725 Net Income (loss): 2020 $ 1,794 $ 2,508 $ 14,804 $ (226,303) 2019 $ 316 $ 7,333 $ 5,513 $ (2,259) Net income (loss) attributable to MDC Partners Inc.: 2020 $ 1,003 $ (593) $ 4,076 $ (233,457) 2019 $ (113) $ 4,290 $ (1,752) $ (7,678) Income (loss) per common share: Basic 2020 $ (0.03) $ (0.06) $ (0.07) $ (3.23) 2019 $ (0.04) $ 0.01 $ (0.07) $ (0.15) Diluted 2020 $ (0.03) $ (0.06) $ (0.07) $ (3.23) 2019 $ (0.04) $ 0.01 $ (0.07) $ (0.15) The above revenue, cost of services sold, and income (loss) have primarily been affected by acquisitions and divestitures. Historically, with some exceptions, the Company’s fourth quarter generates the highest quarterly revenues in a year. The fourth quarter has historically been the period in the year in which the highest volumes of media placements and retail related consumer marketing occur. Income (loss) has been affected as follows: • The fourth quarter of 2020 and 2019 included a foreign exchange gain of $6,274 and a gain of $4,349, respectively. • The fourth quarter of 2020 and 2019 included stock-based compensation charges of $3,611 and $18,408, respectively. • The fourth quarter of 2020 and 2019 included changes in deferred acquisition resulting in income of $41,672 and $9,030, respectively. • The fourth quarter of 2020 and 2019 included goodwill, intangible asset, right-of-use asset, related leasehold improvement impairment charges, and expenses to accelerate the variable costs associated with certain leases of $77,240 and goodwill, right-of-use assets and related leasehold improvement impairment charges of $6,655, respectively.

SCHEDULE II___VALUATION AND QUA

SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2020
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS	SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, (Dollars in Thousands) Column A Column B Column C Column D Column E Column F Description Balance at Charged to Removal of Uncollectible Receivables Translation Adjustments Balance at Valuation accounts deducted from assets to which they apply – allowance for doubtful accounts: December 31, 2020 $ 3,304 $ 3,487 $ (1,305) $ (13) $ 5,473 December 31, 2019 $ 1,879 $ 2,996 $ (1,377) $ (194) $ 3,304 December 31, 2018 $ 2,453 $ 1,538 $ (1,795) $ (317) $ 1,879 Schedule II — 2 of 2 MDC PARTNERS INC. & SUBSIDIARIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, (Dollars in Thousands) Column A Column B Column C Column D Column E Column F Description Balance at Charged to Other Translation Adjustments Balance at Valuation accounts deducted from assets to which they apply – valuation allowance for deferred income taxes: December 31, 2020 $ 65,649 $ 128,938 $ 2,436 $ 1,429 $ 198,452 December 31, 2019 $ 68,479 $ (2,830) $ — $ — $ 65,649 December 31, 2018 $ 19,032 $ 49,447 $ — $ — $ 68,479

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation . The accompanying consolidated financial statements include the accounts of MDC Partners Inc. and its domestic and international controlled subsidiaries that are not considered variable interest entities, and variable interest entities for which the Company is the primary beneficiary. Intercompany balances and transactions have been eliminated in consolidation.
Use of Estimates	Use of Estimates.  The preparation of the consolidated financial statements in conformity with GAAP requires management to make judgments, estimates and assumptions. These estimates and assumptions affect the reported amounts of assets and liabilities including goodwill, intangible assets, contingent deferred acquisition consideration, redeemable noncontrolling interests, deferred tax assets, right-of-use assets and the amounts of revenue and expenses reported during the period. These estimates are evaluated on an ongoing basis and are based on historical experience, current conditions and various other assumptions believed to be reasonable under the circumstances. These estimates require the use of assumptions about future performance, which are uncertain at the time of estimation. To the extent actual results differ from the assumptions used, results of operations and cash flows could be materially affected.
Fair Value	Fair Value.  The Company applies the fair value measurement guidance for financial assets and liabilities that are required to be measured at fair value and for non-financial assets and liabilities that are not required to be measured at fair value on a recurring basis, including goodwill, right-of-use assets and other identifiable intangible assets.
Concentration of Credit Risk	Concentration of Credit Risk . The Company provides marketing communications services to clients who operate in most industry sectors. Credit is granted to qualified clients in the ordinary course of business. Due to the diversified nature of the Company’s client base, the Company does not believe that it is exposed to a concentration of credit risk. No client accounted for more than 10% of the Company’s consolidated accounts receivable as of December 31, 2020 or December 31, 2019. No sales to an individual client or country other than in the United States accounted for more than 10% of revenue for the fiscal years ended December 31, 2020, 2019, or 2018. As the Company operates in foreign markets, it is always considered at least reasonably possible foreign operations will be disrupted in the near term.
Cash and Cash Equivalents	Cash and Cash Equivalents . The Company’s cash equivalents are primarily comprised of investments in overnight interest-bearing deposits, money market instruments and other short-term investments with original maturity dates of three months or less at the time of purchase. The Company has a concentration of credit risk in that there are cash deposits in excess of federally insured amounts.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts . Trade receivables are stated at invoiced amounts less allowances for doubtful accounts. The allowances represent estimated uncollectible receivables associated with potential customer defaults usually due to customers’ potential insolvency. The allowances include amounts for certain customers where a risk of default has been specifically identified. The assessment of the likelihood of customer defaults is based on various factors, including the length of time the receivables are past due, historical experience and existing economic conditions.
Expenditures Billable To Clients	Expenditures Billable to Clients . Expenditures billable to clients consist principally of outside vendor costs incurred on behalf of clients when providing services that have not yet been invoiced to clients. Such amounts are invoiced to clients at various times over the course of the production process.
Fixed Assets	Fixed Assets . Fixed assets are stated at cost, net of accumulated depreciation. Computers, furniture and fixtures are depreciated on a straight-line basis over periods of three to seven years. 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. Repairs and maintenance costs are expensed as incurred.
Leases	Leases . Effective January 1, 2019, the Company adopted Accounting Standards Codification, Leases (“ASC 842”). As a result, the 2018 fiscal year has not been adjusted and continues to be reported under ASC 840, Leases. 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. All right-of-use lease assets are reviewed for impairment. See Note 10 of the Notes to the Consolidated Financial Statements included herein for further information on leases.
Impairment of Long-Lived Assets	Impairment of Long-lived Assets . A long-lived asset or asset group is tested for recoverability whenever events or changes in circumstances indicate that its carrying amount may not be recoverable. When such events occur, the Company compares the sum of the undiscounted cash flows expected to result from the use and eventual disposition of the asset or asset group to the carrying amount of such asset or asset group. If this comparison indicates that there is an impairment, the amount of the impairment is typically calculated using discounted expected future cash flows where observable fair values are not readily determinable. The discount rate applied to these cash flows is based on the Company’s weighted average cost of capital (“WACC”), risk adjusted where appropriate, or other appropriate discount rate.
Equity Method Investments	Equity Method Investments . Equity method investments are investments in entities in which the Company has an ownership interest of less than 50% and has significant influence, or joint control by contractual arrangement, (i) over the operating and financial policies of the affiliate or (ii) has an ownership interest greater than 50%; however, the substantive participating rights of the noncontrolling interest shareholders preclude the Company from exercising unilateral control over the operating and financial policies of the affiliate. The Company ’ s proportionate share of the net income or loss of equity method investments is included in the results of operations and any dividends and distributions reduce the carrying value of the investments. The Company’s equity method investments, include various interests in investment funds. The carrying amount for these investments, which are included in Other assets within the Consolidated Balance Sheets as of December 31, 2020 and 2019 was $3,947 and $6,161, respectively. The Company’s management periodically evaluates these investments to determine if there has been a decline in value that is other than temporary.
Other Investments	Other Investments . From time to time, the Company makes investments in start-ups, such as advertising technology and innovative consumer product companies, where the Company does not exercise significant influence over the operating and financial policies of the investee. Non-marketable equity investments do not have a readily determinable fair value and are recorded at cost, less any impairment, adjusted for qualifying observable investment balance changes. The carrying amount for these investments, which are included in Other assets within the Consolidated Balance Sheets as of December 31, 2020 and 2019 was $7,257 and $9,854, respectively.
Goodwill and Indefinite Lived Intangibles	Goodwill . Goodwill (the excess of the acquisition cost over the fair value of the net assets acquired) acquired as a result of a business combination which is not subject to amortization is tested for impairment, at the reporting unit level, annually as of October 1st of each year, or more frequently if indicators of potential impairment exist. For the annual impairment test, the Company has the option of assessing qualitative factors to determine whether it is more likely than not that the carrying amount of a reporting unit exceeds its fair value or performing a quantitative goodwill impairment test. Qualitative factors considered in the assessment include industry and market considerations, the competitive environment, overall financial performance, changing cost factors such as labor costs, and other factors specific to each reporting unit such as change in management or key personnel. If the Company elects to perform the qualitative assessment and concludes that it is more likely than not that the fair value of the reporting unit is more than its carrying amount, then goodwill is not considered impaired and the quantitative impairment test is not necessary. For reporting units for which the qualitative assessment concludes that it is more likely than not that the fair value of the reporting unit is less than its carrying amount and for reporting units for which the qualitative assessment is not performed, the Company will perform the quantitative impairment test, which compares the fair value of the reporting unit to its carrying amount. If the fair value of the reporting unit exceeds the carrying amount of the net assets assigned to that reporting unit, goodwill is not considered impaired. However, if the fair value of the reporting unit is lower than the carrying amount of the net assets assigned to the reporting unit, an impairment charge is recognized equal to the excess of the carrying amount over the fair value. Determining the fair value of a reporting unit involves the use of significant estimates and assumptions. For the 2020 annual impairment test, the Company used an income approach, which incorporates the use of the discounted cash flow (“DCF”) method. The income approach requires the exercise of significant judgment, including judgment about the amount and timing of expected future cash flows, assumed terminal value and appropriate discount rates.
Definite Lived Intangible Assets	Definite Lived Intangible Assets . Definite lived intangible assets are subject to amortization over their useful lives. The method of amortization selected reflects the pattern in which the economic benefits of the specific intangible asset is consumed or otherwise used. If that pattern cannot be reliably determined, a straight-line amortization method is used over the estimated useful life. Intangible assets that are subject to amortization are reviewed for potential impairment at least annually or whenever events or circumstances indicate that carrying amounts may not be recoverable. For the 2020 annual impairment test, the Company used an income approach, which incorporates the use of the discounted cash flow (“DCF”) method. See Note 8 of the Notes to the Consolidated Financial Statements included herein for further information.
Business Combinations	Business Combinations. Business combinations are accounted for using the acquisition method and accordingly, the assets acquired (including identified intangible assets), the liabilities assumed and any noncontrolling interest in the acquired business are recorded at their acquisition date fair values. For each acquisition, the Company undertakes a detailed review to identify other intangible assets and a valuation is performed for all such identified assets. The Company uses several market participant measurements to determine the estimated value. This approach includes consideration of similar and recent transactions, as well as utilizing discounted expected cash flow methodologies. A substantial portion of the intangible assets value that the Company acquires is the specialized know-how of the workforce, which is treated as part of goodwill and is not required to be valued separately. The majority of the value of the identifiable intangible assets acquired is derived from customer relationships, including the related customer contracts, as well as trademarks.
Deferred Acquisition Consideration	Deferred Acquisition Consideration . Most acquisitions include an initial payment at the time of closing and provide for future additional contingent purchase price payments. Contingent purchase price obligations for these transactions are recorded as deferred acquisition consideration liabilities, and are derived from the projected performance of the acquired entity and are
Redeemable Noncontrolling Interest	Redeemable Noncontrolling Interests . Many of the Company’s acquisitions include contractual arrangements where the noncontrolling shareholders have an option to purchase, or may require the Company to purchase, such noncontrolling shareholders’ incremental ownership interests under certain circumstances. The Company has similar call options under the same contractual terms. The amount of consideration under these contractual arrangements is not a fixed amount, but rather is dependent upon various valuation formulas, such as the average earnings of the relevant subsidiary through the date of exercise or the growth rate of the earnings of the relevant subsidiary during that period. In the event that an incremental purchase may be required by the Company, the amounts are recorded as redeemable noncontrolling interests in mezzanine equity on the Consolidated Balance Sheets at their acquisition date fair value and adjusted for changes to their estimated redemption value through Common stock and other paid-in capital in the Consolidated Balance Sheets (but not less than their initial redemption value), except for foreign currency translation adjustments. These adjustments will not impact the calculation of earnings (loss) per share if the redemption values are less than the estimated fair values. See Note 13 of the Notes to the Consolidated Financial Statements for detail on the impact on the Company’s earnings (loss) per share calculation.
Subsidiary and Equity Investment Stock Transactions	Subsidiary and Equity Investment Stock Transactions. Transactions involving the purchase, sale or issuance of stock of a subsidiary where control is maintained are recorded as a reduction in the redeemable noncontrolling interests or noncontrolling interests, as applicable. Any difference between the purchase price and noncontrolling interest is recorded to Common stock and other paid-in capital in the Consolidated Balance Sheets. In circumstances where the purchase of shares of an equity investment results in obtaining control, the existing carrying value of the investment is remeasured to the acquisition date fair value and any gain or loss is recognized in the results of operations.
Revenue Recognition	Revenue Recognition . The Company’s 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. See Note 5 of the Notes to the Consolidated Financial Statements included herein for additional information.
Cost of Services Sold	Cost of Services Sold . Cost of services sold primarily consists of staff costs, and does not include depreciation charges for fixed assets.
Interest Expense	Interest Expense.  The Company uses the effective interest method to amortize deferred financing costs and any original issue premium or discount, if applicable. The Company also uses the straight-line method, which approximates the effective interest method, to amortize the deferred financing costs on the Credit Agreement.
Income Taxes	Income Taxes. We account for income taxes using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized based on the differences between the financial statement carrying value of existing assets and liabilities and their respective tax bases. Deferred tax assets and liabilities are measured using enacted tax rates and laws expected to be in effect when the differences are expected to reverse. The Company records associated interest and penalties as a component of income tax expense.The Company records a valuation allowance against deferred income tax assets when management believes it is more likely than not that some portion or all of the deferred income tax assets will not be realized. Management evaluates on a quarterly basis all available positive and negative evidence considering factors such as the reversal of deferred income tax liabilities, taxable income in eligible carryback years, projected future taxable income, the character of the income tax asset, tax planning strategies, changes in tax laws and other factors. The periodic assessment of the net carrying value of the Company’s deferred tax assets under the applicable accounting rules requires significant management judgment. A change to any of these factors could impact the estimated valuation allowance and income tax expense.
Share-based Compensation	Stock-Based Compensation . Under the fair value method, compensation cost is measured at fair value at the date of grant and is expensed over the service period, generally the award’s vesting period. The Company uses its historical volatility derived over the expected term of the award to determine the volatility factor used in determining the fair value of the award. The Company recognizes forfeitures as they occur. Stock-based awards that are settled in cash or equity at the option of the Company are recorded at fair value on the date of grant. The fair value measurement of the compensation cost for these awards is based on using the Black-Scholes option pricing-model or other acceptable method and is recorded in Operating income over the service period, in this case the award’s vesting period. The Company has adopted the straight-line attribution method for determining the compensation cost to be recorded during each accounting period. The Company commences recording compensation expense related to awards that are based on performance conditions under the straight-line attribution method when it is probable that such performance conditions will be met.
Reitrement Costs	Retirement Costs . Several of the Company’s subsidiaries offer employees access to certain defined contribution retirement programs. Under the defined contribution plans, these subsidiaries, in some cases, make annual contributions to participants’ accounts which are subject to vesting. The Company’s contribution expense pursuant to these plans was $8,203, $11,909 and $11,136 for the years ended December 31, 2020, 2019, and 2018, respectively. The Company also has a defined benefit pension plan. See Note 12 of the Notes to the Consolidated Financial Statements included herein for additional information on the defined benefit plan.
Income (Loss) per Common Share	Income (Loss) per Common Share . Basic income (loss) per common share is based upon the weighted average number of common shares outstanding during each period. Diluted income (loss) per common share is based on the above, in addition, if dilutive, common share equivalents, which include outstanding options, stock appreciation rights, and unvested restricted stock units. In periods of net loss, all potentially issuable common shares are excluded from diluted net loss per common share because they are anti-dilutive. The Company has 145,000 authorized and issued convertible preference shares. The two-class method is applied to calculate basic net income (loss) attributable to MDC Partners Inc. per common share in periods in which shares of convertible preference shares are outstanding, as shares of convertible preference shares are participating securities due to their dividend rights. See Note 15 of the Notes to the Consolidated Financial Statements included herein for additional information. The two-class method is an earnings allocation method under which earnings per share is calculated for common stock considering a participating security’s rights to undistributed earnings as if all such earnings had been distributed during the period. Either the two-class method or the if-converted method is applied to calculate diluted net income per common share, depending on which method results in more dilution. The Company’s participating securities are not included in the computation of net loss per common share in periods of net loss because the convertible preference shareholders have no contractual obligation to participate in losses.
Foreign Currency Translation	Foreign Currency Translation . The functional currency of the Company is the Canadian dollar; however, it has decided to use U.S. dollars as its reporting currency for consolidated reporting purposes. Generally, the Company’s subsidiaries use their local currency as their functional currency. Accordingly, the currency impacts of the translation of the Consolidated Balance Sheets of the Company and its non-U.S. dollar based subsidiaries to U.S. dollar statements are included as cumulative translation adjustments in Accumulated other comprehensive income (loss). Translation of intercompany debt, which is not intended to be repaid, is included in cumulative translation adjustments. Cumulative translation adjustments are not included in net earnings (loss) unless they are actually realized through a sale or upon complete, or substantially complete, liquidation of the Company’s net investment in the foreign operation. Translation of current intercompany balances are included in net earnings (loss). The balance sheets of non-U.S. dollar based subsidiaries are translated at the period end rate. The Consolidated Statements of Operation of the Company and its non-U.S. dollar based subsidiaries are translated at average exchange rates for the period. Gains and losses arising from the Company’s foreign currency transactions are reflected in net earnings. Unrealized gains or losses arising on the translation of certain intercompany foreign currency transactions that are of a long-term nature (that is settlement is not planned or anticipated in the future) are included as cumulative translation adjustments in Accumulated other comprehensive (loss) income.
New Accounting Pronouncements	New Accounting Pronouncement In December 2019, the FASB issued ASU 2019-12, Income Taxes, to simplify the accounting for income taxes, including amending the rules for performing intra-period tax allocations and calculating income taxes in interim periods, the accounting for transactions that result in a step-up in the tax basis of goodwill, as well as other amendments. ASU 2019-12 is effective January 1, 2021. We do not expect the adoption of ASU 2019-12 will have a material effect on our results of operations and financial position.

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2020
By Location
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	The following table presents revenue disaggregated by geography for the twelve months ended December 31, 2020, 2019 and 2018: Twelve Months Ended December 31, Geographic Location Reportable Segment 2020 2019 2018 United States All $ 959,636 $ 1,116,045 $ 1,152,399 Canada All 81,930 105,067 124,001 Other All 157,445 194,691 198,688 $ 1,199,011 $ 1,415,803 $ 1,475,088
Industry Vertical
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	The following table presents revenue disaggregated by client industry vertical for the twelve months ended December 31, 2020, 2019 and 2018: Twelve Months Ended December 31, Industry Reportable Segment 2020 2019 2018 Food & Beverage All $ 205,939 $ 280,094 $ 313,368 Retail All 148,293 148,851 152,552 Consumer Products All 165,105 167,324 162,524 Communications All 77,443 184,870 178,410 Automotive All 67,339 78,985 88,807 Technology All 181,057 118,169 104,479 Healthcare All 100,727 102,221 127,547 Financials All 91,438 112,351 110,069 Transportation and Travel/Lodging All 44,510 88,958 86,419 Other All 117,160 133,980 150,913 $ 1,199,011 $ 1,415,803 $ 1,475,088

Income (Loss) Per Common Share

Income (Loss) Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2020
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 loss per common share: Twelve Months Ended December 31, 2020 2019 2018 Numerator: Net loss attributable to MDC Partners Inc. $ (228,971) $ (5,253) $ (130,007) Accretion on convertible preference shares (14,179) (12,304) (8,355) Net loss attributable to MDC Partners Inc. common shareholders $ (243,150) $ (17,557) $ (138,362) Denominator: Basic weighted average number of common shares outstanding 72,862,178 69,132,100 57,218,994 Dilutive effect of equity awards — — — Diluted weighted average number of common shares outstanding 72,862,178 69,132,100 57,218,994 Basic $ (3.34) $ (0.25) $ (2.42) Diluted $ (3.34) $ (0.25) $ (2.42)

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following is a summary of the Company’s fixed assets as of December 31: 2020 2019 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 93,850 $ (74,766) $ 19,084 $ 93,224 $ (69,687) $ 23,537 Leasehold improvements 132,729 (61,400) 71,329 117,409 (59,892) 57,517 $ 226,579 $ (136,166) $ 90,413 $ 210,633 $ (129,579) $ 81,054

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	As of December 31, goodwill was as follows: Goodwill Integrated Networks - Group A Integrated Networks -Group B Media & Data Network All Other Total Balance at December 31, 2018 $ 139,452 $ 267,059 $ 101,768 $ 224,473 $ 732,752 Acquired goodwill — 1,025 — — 1,025 Impairment loss recognized (4,879) — — — (4,879) Transfer of goodwill between segments (1) — (120) 3,612 (3,492) — Foreign currency translation — 423 217 2,153 2,793 Balance at December 31, 2019 $ 134,573 $ 268,387 $ 105,597 $ 223,134 $ 731,691 Acquired goodwill — — — — — Disposition — — — (7,074) (7,074) Impairment loss recognized — (16,137) (5,287) (40,237) (61,661) Transfer of goodwill between segments — 19,696 4,546 (24,242) — Foreign currency translation — 212 538 4,505 5,255 Balance at December 31, 2020 $ 134,573 $ 272,158 $ 105,394 $ 156,086 $ 668,211 (1) Transfers of goodwill relate to changes in segments.
Schedule of Intangible Assets and Goodwill	The gross and net amounts of acquired intangible assets other than goodwill as of December 31, Intangible Assets 2020 2019 Trademark (indefinite life) $ — $ 14,600 Customer relationships – gross $ 52,594 $ 58,211 Less accumulated amortization (32,667) (32,671) Customer relationships – net $ 19,927 $ 25,540 Trademarks (definite life) – gross $ 32,711 $ 28,695 Less accumulated amortization (18,794) (13,942) Trademarks (definite life) – net $ 13,917 $ 14,753 Total intangible assets $ 85,305 $ 101,506 Less accumulated amortization (51,461) (46,613) Total intangible assets – net $ 33,844 $ 54,893
Finite-lived Intangible Assets Amortization Expense	The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2021 $ 8,514 2022 8,062 2023 7,711 2024 4,558 Thereafter 4,999

Deferred Acquisition Consider_2

Deferred Acquisition Consideration (Tables)	12 Months Ended
	Dec. 31, 2020
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 December 31, 2020 and December 31, 2019. December 31, 2020 2019 Beginning balance of contingent payments $ 74,671 $ 82,598 Payments (46,792) (30,719) Redemption value adjustments (1) 44,993 15,451 Additions - acquisitions and step-up transactions 7,703 7,145 Other 2,227 196 Ending balance of contingent payments $ 82,802 $ 74,671 Fixed payments 263 549 $ 83,065 $ 75,220 (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 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 for the twelve months ended December 31, 2020 and 2019: 2020 2019 Loss attributable to fair value adjustments $ 42,187 $ 5,403 Stock-based compensation 2,806 10,048 Redemption value adjustments $ 44,993 $ 15,451

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Lease Costs and Other Quantitative Information	The following table presents lease costs and other quantitative information for the twelve months ended December 31: Twelve Months Ended December 31, Twelve Months Ended December 31, 2020 2019 Lease Cost: Operating lease cost $ 71,257 $ 67,044 Variable lease cost 14,640 18,879 Sublease rental income (11,329) (8,965) Total lease cost $ 74,568 $ 76,958 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 70,277 $ 69,735 Right-of-use assets obtained in exchange for operating lease liabilities and other non-cash adjustments $ 45,663 $ 269,801 Weighted average remaining lease term (in years) - Operating leases 7.2 5.3 Weighted average discount rate - Operating leases 10.6 8.6
Minimum Future Rental Payments	The following table presents minimum future rental payments under the Company’s leases at December 31, 2020 and their reconciliation to the corresponding lease liabilities: Maturity Analysis 2021 $ 68,375 2022 60,252 2023 56,842 2024 49,909 2025 38,880 2026 and thereafter 150,950 Total 425,208 Less: Present value discount (136,757) Lease liability $ 288,451

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Schedule of Debt [Table Text Block]	As of December 31, 2020 and 2019, the Company’s indebtedness was comprised as follows: December 31, 2020 December 31, 2019 Revolving credit agreement $ — $ — Senior Notes 870,256 900,000 Debt issuance costs (27,072) (12,370) $ 843,184 $ 887,630

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2020
Retirement Benefits [Abstract]
Schedule of Net Periodic Benefit Cost Not yet Recognized	Net periodic pension cost consists of the following components for the years ended December 31: Pension Benefits 2020 2019 2018 Service cost $ — $ — $ — Interest cost on benefit obligation 1,426 1,640 1,641 Expected return on plan assets (1,924) (1,604) (1,948) Curtailment and settlements 2,333 626 1,039 Amortization of actuarial (gains) losses 340 266 258 Net periodic benefit cost $ 2,175 $ 928 $ 990
Schedule Of Assumptions Used To Determine Net Periodic Cost	The following weighted average assumptions were used to determine net periodic costs at December 31: Pension Benefits 2020 2019 2018 Discount rate 3.39 % 4.42 % 3.83 % Expected return on plan assets 7.00 % 7.00 % 7.00 % Rate of compensation increase N/A N/A N/A
Schedule of Defined Benefit Plan Amounts Recognized in Other Comprehensive Income (Loss)	Other changes in plan assets and benefit obligation recognized in Other comprehensive income (loss) consist of the following components for the years ended December 31: Pension Benefits 2020 2019 2018 Current year actuarial (gain) loss $ 2,213 $ 2,917 $ (520) Amortization of actuarial loss (340) (266) (258) Total recognized in other comprehensive (income) loss 1,873 2,651 (778) Total recognized in net periodic benefit cost and other comprehensive loss $ 4,048 $ 3,579 $ 212
Schedule of Benefit Obligations in Excess of Fair Value of Plan Assets	The following table summarizes the change in benefit obligations and fair values of plan assets for the years ended December 31: 2020 2019 2018 Change in benefit obligation: Benefit obligation, Beginning balance $ 43,012 $ 37,938 $ 43,750 Interest Cost 1,426 1,640 1,641 Actuarial (gains) losses 5,301 6,127 (3,522) Benefits paid (6,728) (2,693) (3,931) Benefit obligation, Ending balance 43,011 43,012 37,938 Change in plan assets: Fair value of plan assets, Beginning balance 27,206 23,181 27,977 Actual return on plan assets 2,678 4,188 (2,093) Employer contributions 2,325 2,530 1,228 Benefits paid (6,728) (2,693) (3,931) Fair value of plan assets, Ending balance 25,481 27,206 23,181 Unfunded status $ 17,530 $ 15,806 $ 14,757
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the balance sheet at December 31 consist of the following: Pension Benefits 2020 2019 Non-current liability $ 17,530 $ 15,806 Net amount recognized $ 17,530 $ 15,806
Schedule of Amounts Recognized in Other Comprehensive Income (Loss)	Amounts recognized in Accumulated Other Comprehensive Loss before income taxes consists of the following components for the years ended December 31: Pension Benefits 2020 2019 Accumulated net actuarial losses $ 17,403 $ 15,530 Amount recognized $ 17,403 $ 15,530
Schedule Of Assumptions Used To Determine Benefit Obligations	The following weighted average assumptions were used to determine benefit obligations as of December 31: Pension Benefits 2020 2019 Discount rate 2.55 % 3.39 % Rate of compensation increase N/A N/A
Schedule of Changes in Fair Value of Plan Assets	The fair value of the plan assets as of December 31, is as follows: December 31, 2020 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,039 $ 1,039 $ — $ — Mutual funds 24,442 24,442 — — Total $ 25,481 $ 25,481 $ — $ — December 31, 2019 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,275 $ 1,275 $ — $ — Mutual funds 25,931 25,931 — — Total $ 27,206 $ 27,206 $ — $ —
Schedule of Allocation of Plan Assets	The pension plans weighted-average asset allocation for the years ended December 31, 2020 and 2019 are as follows: Target Allocation Actual Allocation 2020 2020 2019 Asset Category: Equity securities 65.0 % 69.0 % 66.7 % Debt securities 30.0 % 27.0 % 28.6 % Cash/cash equivalents and Short term investments 5.0 % 4.0 % 4.7 % 100.0 % 100.0 % 100.0 %
Schedule of Expected Benefit Payments	The following estimated benefit payments, which reflect expected future service, as appropriate, are expected to be paid in the years ending December 31: Period Amount 2021 $ 1,802 2022 1,769 2023 1,983 2024 2,231 2025 2,171 Thereafter 10,796

Noncontrolling and Redeemable_2

Noncontrolling and Redeemable Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2020
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 Consolidated Balance Sheets for the twelve months ended December 31, 2020 and 2019 were as follows: Noncontrolling Balance, December 31, 2018 $ 9,278 Income attributable to noncontrolling interests 16,156 Distributions made (11,392) Other (14) Balance, December 31, 2019 $ 14,028 Income attributable to noncontrolling interests 21,774 Distributions made (15,192) Other 94 Balance, December 31, 2020 $ 20,704
Noncontrolling Interest [Table Text Block]	Changes in the Company’s ownership interests in our less than 100% owned subsidiaries during the three years ended December 31, were as follows: Years Ended December 31, 2020 2019 2018 Net loss attributable to MDC Partners Inc. $ (228,971) $ (5,253) $ (130,007) Transfers from the noncontrolling interest: Increase in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests 1,626 1,911 10,140 Net transfers from noncontrolling interests $ 1,626 $ 1,911 $ 10,140 Change from net loss attributable to MDC Partners Inc. and transfers to noncontrolling interests $ (227,345) $ (3,342) $ (119,867)
Redeemable Noncontrolling Interest [Table Text Block]	The following table presents changes in redeemable noncontrolling interests as of December 31, 2020 and 2019: Years Ended December 31, 2020 2019 Beginning Balance $ 36,973 $ 51,546 Redemptions (12,289) (14,530) Granted — — Changes in redemption value 2,800 (3,163) Currency translation adjustments (347) 3 Other — 3,117 Ending Balance $ 27,137 $ 36,973

Share Capital Share Capital (Ta

Share Capital Share Capital (Tables)	12 Months Ended
	Dec. 31, 2020
Share Capital [Abstract]
Schedule Of Share Based Compensation Performance Shares And Time Based Award Activity	The following table summarizes information about financial performance based and time based restricted stock and restricted stock unit awards: Performance-Based Awards Time-Based Awards Shares Weighted Average Grant Date Fair Shares Weighted Average Balance at December 31, 2019 2,443,801 $ 3.11 568,960 $ 5.53 Granted 685,369 2.19 1,741,280 1.97 Vested (555,226) 2.96 (1,031,159) 3.39 Forfeited (336,950) 3.07 (141,821) 3.32 Balance at December 31, 2020 2,236,994 $ 3.37 1,137,260 $ 2.29
Share-based Compensation, Stock Options, Activity	The following table summarizes information about share option awards: Share Option Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2019 111,866 $ 2.23 $ 4.85 Granted — — — Forfeited (111,866) 2.23 4.85 Exercised — — — Balance at December 31, 2020 — $ — $ —
Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity	The following table summarizes information about stock appreciation rights (“SAR”) awards: SAR Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2019 2,325,800 $ 1.14 $ 3.07 Granted — — — Forfeited (250,000) 0.73 5.00 Exercised — — — Balance at December 31, 2020 2,075,800 $ 1.19 $ 2.84

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2020
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes in accumulated other comprehensive income (loss) for the twelve months ended December 31 were: Defined Foreign Currency Translation Total Balance December 31, 2018 $ (13,101) $ 17,821 $ 4,720 Other comprehensive income before reclassifications — (7,078) (7,078) Amounts reclassified from accumulated other comprehensive loss (net of tax benefit of $740) (1,911) — (1,911) Other comprehensive income (1,911) (7,078) (8,989) Balance December 31, 2019 $ (15,012) $ 10,743 $ (4,269) Other comprehensive loss before reclassifications — 8,362 8,362 Amounts reclassified from accumulated other comprehensive loss (net of tax benefit of $519) (1,354) — (1,354) Other comprehensive loss (1,354) 8,362 7,008 Balance December 31, 2020 $ (16,366) $ 19,105 $ 2,739

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The components of the Company’s income (loss) before income taxes and equity in earnings of non-consolidated affiliates by taxing jurisdiction for the years ended December 31, were: 2020 2019 2018 Income (Loss): U.S. $ (73,227) $ (17,491) $ (76,960) Non-U.S. (15,175) 38,358 (11,709) $ (88,402) $ 20,867 $ (88,669)
Schedule Of Components Of Income Taxes Provision Benefit	The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2020 2019 2018 Current tax provision U.S. federal $ 3,016 $ 2,638 $ 444 U.S. state and local 742 12 2 Non-U.S. 4,241 2,875 7,584 7,999 5,525 8,030 Deferred tax provision (benefit): U.S. federal 75,686 4,635 (10,817) U.S. state and local 34,404 1,130 (3,476) Non-U.S. (1,534) (974) 35,878 108,556 4,791 21,585 Income tax expense (benefit) $ 116,555 $ 10,316 $ 29,615
Schedule of Effective Income Tax Rate Reconciliation	A reconciliation of income tax expense (benefit) using the U.S. federal income tax rate compared with actual income tax expense for the years ended December 31, is as follows: 2020 2019 2018 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ (88,402) $ 20,867 $ (88,669) Statutory income tax rate 21.0 % 21.0 % 21.0 % Tax expense (benefit) using U.S. statutory income tax rate (18,564) 4,382 (18,621) State and foreign taxes (3,486) 1,496 (3,944) Non-deductible stock-based compensation 1,162 3,823 1,512 Global intangible low-taxed income 1,363 1,147 710 Base erosion and anti-abuse tax 4,697 2,504 389 Other non-deductible expense 1,043 273 1,388 Change to valuation allowance 128,938 (2,830) 49,482 Effect of the difference in U.S. federal and local statutory rates 67 1,422 (152) Noncontrolling interests (4,649) (3,566) (2,674) Other impacts of foreign operations 1,160 2,724 612 Impact of goodwill impairments 10,158 436 8,703 Adjustments to accrued taxes in previous periods 4,641 (3,544) 1,192 Adjustment to deferred tax balances* (9,999) 1,920 (8,845) Other, net 24 129 (137) Income tax expense (benefit) $116,555 $10,316 $29,615 Effective income tax rate (131.8)% 49.4% (33.4)%
Schedule of Deferred Tax Assets and Liabilities	The tax effects of significant temporary differences representing deferred tax assets and liabilities at December 31, were as follows: 2020 2019 Deferred tax assets: Accounting reserves and other $ 20,831 $ 10,987 Net operating loss carryforwards 47,139 60,705 Interest deductions 20,819 16,797 Refinancing charge — 669 Goodwill and intangibles 122,045 117,421 Stock compensation 1,693 1,736 Pension plan 4,856 4,414 Unrealized foreign exchange 11,995 11,373 Capital loss carryforwards 13,657 13,081 Lease liabilities 77,870 76,397 Gross deferred tax asset 320,905 313,580 Less: valuation allowance (198,452) (65,649) Net deferred tax assets 122,453 247,931 Deferred tax liabilities: Right-of-use assets $ (57,890) $ (67,613) Refinancing charge (1,675) — Withholding taxes (475) (546) Capital assets (1,893) (382) Goodwill amortization (88,326) (98,677) Total deferred tax liabilities (150,259) (167,218) Net deferred tax asset (liability) $ (27,806) $ 80,713 Deferred tax assets $ 179 $ 84,900 Deferred tax liabilities (27,985) (4,187) $ (27,806) $ 80,713
Schedule Of Changes In Tax Reserve	If these unrecognized tax benefits were to be recognized, it would affect the Company’s effective tax rate. 2020 2019 2018 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 996 $ 887 $ 1,433 Current year positions 581 275 — Prior period positions — — 7 Settlements — — (314) Lapse of statute of limitations (170) (166) (239) Unrecognized tax benefits - Ending Balance $ 1,407 $ 996 $ 887

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
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 December 31, 2020 and 2019: December 31, 2020 December 31, 2019 Carrying Fair Value Carrying Fair Value Liabilities: Senior Notes $ 870,256 $ 883,580 $ 900,000 $ 812,250

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2020
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Years Ended December 31, 2020 2019 2018 Revenue: Integrated Networks - Group A $ 379,648 $ 392,101 $ 393,890 Integrated Networks - Group B 435,589 531,717 551,317 Media & Data Network 139,015 161,451 183,287 All Other 244,759 330,534 346,594 Total $ 1,199,011 $ 1,415,803 $ 1,475,088 Adjusted EBITDA: Integrated Networks - Group A $ 79,793 $ 74,822 $ 75,609 Integrated Networks - Group B 84,297 84,568 74,091 Media & Data Network 9,707 7,746 12,205 All Other 30,755 37,618 38,307 Corporate (27,220) (30,601) (38,761) Total Adjusted EBITDA $ 177,332 $ 174,153 $ 161,451 Depreciation and amortization $ (36,905) $ (38,329) $ (46,196) Impairment and other losses (96,399) (8,599) (87,204) Stock compensation expense (14,179) (31,040) (18,416) Deferred acquisition consideration expense/(income) (42,187) (5,403) 457 Loss on investments (2,175) (2,048) (779) Other expense (31,244) (9,274) (7,879) Total Operating Income (Loss) $ (45,757) $ 79,460 $ 1,434 Other Income (Expenses): Interest expense and finance charges, net $ (62,163) $ (64,942) $ (67,075) Foreign exchange gain (loss) (982) 8,750 (23,258) Other, net 20,500 (2,401) 230 Income (loss) before income taxes and equity in earnings of non-consolidated affiliates (88,402) 20,867 (88,669) Income tax expense 116,555 10,316 29,615 Income (loss) before equity in earnings of non-consolidated affiliates (204,957) 10,551 (118,284) Equity in earnings of non-consolidated affiliates (2,240) 352 62 Net income (loss) (207,197) 10,903 (118,222) Net income attributable to the noncontrolling interest (21,774) (16,156) (11,785) Net loss attributable to MDC Partners Inc. (228,971) (5,253) (130,007) Accretion on and net income allocated to convertible preference shares (14,179) (12,304) (8,355) Net loss attributable to MDC Partners Inc. common shareholders $ (243,150) $ (17,557) $ (138,362) Years Ended December 31, 2020 2019 2018 Depreciation and amortization: (Dollars in Thousands) Integrated Networks - Group A $ 6,467 $ 8,559 $ 9,602 Integrated Networks - Group B 17,204 15,904 19,032 Media & Data Network 4,376 4,303 3,820 All Other 7,478 8,695 12,980 Corporate 1,380 868 762 Total $ 36,905 $ 38,329 $ 46,196 Stock-based compensation: Integrated Networks - Group A $ 7,580 $ 24,420 $ 5,792 Integrated Networks - Group B 3,191 4,303 6,890 Media & Data Network 122 63 320 All Other 304 374 755 Corporate 2,982 1,880 4,659 Total $ 14,179 $ 31,040 $ 18,416 Capital expenditures: Integrated Networks - Group A $ 1,087 $ 5,934 $ 8,228 Integrated Networks - Group B 987 9,270 6,352 Media & Data Network 569 627 1,632 All Other 966 2,729 3,985 Corporate 33,694 36 67 Total $ 37,303 $ 18,596 $ 20,264

Quarterly Results of Operatio_2

Quarterly Results of Operations (Tables)	12 Months Ended
	Dec. 31, 2020
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Table Text Block]	The following table sets forth a summary of the Company’s consolidated unaudited quarterly results of operations for the years ended December 31, in thousands of dollars, except per share amounts. Quarters First Second Third Fourth Revenue: 2020 $ 327,742 $ 259,678 $ 283,423 $ 328,168 2019 $ 328,791 $ 362,130 $ 342,907 $ 381,975 Cost of services sold: 2020 $ 222,693 $ 165,632 $ 172,531 $ 209,043 2019 $ 237,154 $ 240,749 $ 222,448 $ 260,725 Net Income (loss): 2020 $ 1,794 $ 2,508 $ 14,804 $ (226,303) 2019 $ 316 $ 7,333 $ 5,513 $ (2,259) Net income (loss) attributable to MDC Partners Inc.: 2020 $ 1,003 $ (593) $ 4,076 $ (233,457) 2019 $ (113) $ 4,290 $ (1,752) $ (7,678) Income (loss) per common share: Basic 2020 $ (0.03) $ (0.06) $ (0.07) $ (3.23) 2019 $ (0.04) $ 0.01 $ (0.07) $ (0.15) Diluted 2020 $ (0.03) $ (0.06) $ (0.07) $ (3.23) 2019 $ (0.04) $ 0.01 $ (0.07) $ (0.15)

Basis of Presentation and Rec_2

Basis of Presentation and Recent Developments Basis of Presentation and Recent Developments (Details) - Definitive Transaction Agreement - USD ($)	Dec. 21, 2020	Dec. 20, 2020
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Membership interests to be exchanged under Transaction Agreement (shares)	216,250,000
Cash to be contributed for each new share of Class C series of common stock	$ 100
Exchange ratio	1
Conversion price (usd per share)	$ 5	$ 7.42
Extended accretion period	2 years
Accretion rate (percent)	6.00%
Shares that can be redeemed	$ 30,000,000
Subordinate note or loan that can be issued in exchange of redeemable shares	$ 25,000,000
Subordinate note or loan, maturity period	3 years
Exchange discount to face value (percent)	17.00%
Interest rate, stated percentage	8.00%
Debt Instrument, Interest Rate, Increase (Decrease)	1.00%
Consent fee (percent)	2.00%
Consent fee upon supplemental indenture (percent)	3.00%
Class A
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resulting interest to be held in combined entity (percent)	26.00%
Class B
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resulting interest to be held in combined entity (percent)	26.00%
Class C
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Resulting interest to be held in combined entity (percent)	74.00%

Significant Accounting Polici_3

Significant Accounting Policies - Narrative (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Equity method investments	$ 3,947	$ 6,161
Other investments	7,257	9,854
Defined contribution plan, expense	$ 8,203	$ 11,909	$ 11,136
Preference shares, authorized (in shares)	145,000	145,000	95,000

New Accounting Pronouncements (

New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Lease liability	$ 288,451
Operating lease right-of-use asset	$ 214,188	$ 223,622

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details Textual) - USD ($) $ in Thousands	Jul. 01, 2020	Mar. 19, 2020	Feb. 14, 2020	Nov. 15, 2019	Apr. 01, 2019	Mar. 08, 2019	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Deferred acquisition consideration							$ 83,065	$ 75,220
Redemptions							$ 12,289	$ 14,530
Veritas
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)	10.00%
Aggregate purchase price	$ 2,187
Closing cash payment	1,087
Business acquisitions and step-up transactions, net of tax	(2,651)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value	$ 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
Business acquisitions and step-up transactions, net of tax		(1,615)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value		$ 503
Laird - Partners [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)				35.00%
Aggregate purchase price				$ 2,389
Closing cash payment				1,588
Deferred acquisition consideration				801
Business acquisitions and step-up transactions, net of tax				(5,045)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value				$ 2,656
Hunter PR LLC [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)					35.00%
Aggregate purchase price					$ 10,234
Closing cash payment					3,890
Deferred acquisition consideration					6,344
Business acquisitions and step-up transactions, net of tax					(9,486)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value					$ 745
Kingsdale Partners LP [Member]
Business Acquisition [Line Items]
Proceeds from divestiture of businesses						$ 50,000
Gain (loss) on disposal						3,000
Gain on disposition of business						$ 3,000
Sloane and Company LLC
Business Acquisition [Line Items]
Proceeds from divestiture of businesses			$ 26,696
Gain (loss) on disposal			16,827
Gain on disposition of business			$ 16,827

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Services	$ 328,168	$ 283,423	$ 259,678	$ 327,742	$ 381,975	$ 342,907	$ 362,130	$ 328,791	$ 1,199,011	$ 1,415,803	$ 1,475,088
United States
Disaggregation of Revenue [Line Items]
Services									959,636	1,116,045	1,152,399
Canada
Disaggregation of Revenue [Line Items]
Services									81,930	105,067	124,001
Other
Disaggregation of Revenue [Line Items]
Services									157,445	194,691	198,688
Food & Beverage
Disaggregation of Revenue [Line Items]
Services									205,939	280,094	313,368
Retail
Disaggregation of Revenue [Line Items]
Services									148,293	148,851	152,552
Consumer Products
Disaggregation of Revenue [Line Items]
Services									165,105	167,324	162,524
Communications
Disaggregation of Revenue [Line Items]
Services									77,443	184,870	178,410
Automotive
Disaggregation of Revenue [Line Items]
Services									67,339	78,985	88,807
Technology
Disaggregation of Revenue [Line Items]
Services									181,057	118,169	104,479
Healthcare
Disaggregation of Revenue [Line Items]
Services									100,727	102,221	127,547
Financials
Disaggregation of Revenue [Line Items]
Services									91,438	112,351	110,069
Transportation and Travel/Lodging
Disaggregation of Revenue [Line Items]
Services									44,510	88,958	86,419
Other
Disaggregation of Revenue [Line Items]
Services									$ 117,160	$ 133,980	$ 150,913

Revenue - Contract Assets and L

Revenue - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Unbilled service fees	$ 49,110	$ 65,004
Unbilled outside vendor costs, billable to clients	10,552	30,133
Capitalized Contract Cost [Line Items]
Advance billings	112,755	216,931
Decrease in deferred revenues	104,176
Revenue recognized	210,078
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Amount	$ 6,105
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, Percentage	92.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
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, Percentage	8.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year
Advance Billings [Member]
Capitalized Contract Cost [Line Items]
Advance billings	$ 152,956	$ 171,742
Decrease in deferred revenues	(18,786)
Revenue recognized	$ 152,361

Income (Loss) Per Common Shar_2

Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Net loss attributable to MDC Partners Inc.	$ (233,457)	$ 4,076	$ (593)	$ 1,003	$ (7,678)	$ (1,752)	$ 4,290	$ (113)	$ (228,971)	$ (5,253)	$ (130,007)
Numerator
Net loss attributable to MDC Partners Inc. common shareholders									(243,150)	(17,557)	(138,362)
Income (Loss) from Continuing Operations Attributable to Parent, Diluted									$ (243,150)	$ (17,557)	$ (138,362)
Denominator
Denominator for basic income (loss) per common share - weighted average common shares									72,862,178	69,132,100	57,218,994
Weighted Average Number Diluted Shares Outstanding Adjustment									0	0	0
Denominator for diluted income (loss) per common share - adjusted weighted shares and assumed conversions									72,862,178	69,132,100	57,218,994
Earnings per share, basic									$ (3.34)	$ (0.25)	$ (2.42)
Earnings per share, diluted									$ (3.34)	$ (0.25)	$ (2.42)
Series 4 Convertible Preferred Stock | Convertible Preference Shares
Numerator
Accretion on and net income allocated to convertible preference shares									$ (14,179)	$ (12,304)	$ (8,355)
Denominator
Antidilutive securities excluded from computation of earnings per share (shares)									5,341,846,000	5,450,426,000	1,442,518,000

Income (Loss) Per Common Shar_3

Income (Loss) Per Common Share (Details Textual) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
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)	642,837	135,386	1,012,637
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)	5,341,846,000	5,450,426,000	1,442,518,000
Shares outstanding (shares)	145,000,000	145,000,000	95,000,000	95,000,000
Convertible preferred stock, common shares issuable upon conversion (shares)	28,853,621	26,656,285	10,970,714

Fixed Assets - Schedule of Fixe

Fixed Assets - Schedule of Fixed Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Cost	$ 226,579	$ 210,633
Accumulated Depreciation	(136,166)	(129,579)	$ (128,546)
Net Book Value	90,413	81,054
Computers, furniture and fixtures
Property, Plant and Equipment [Line Items]
Cost	93,850	93,224
Accumulated Depreciation	(74,766)	(69,687)
Net Book Value	19,084	23,537
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Cost	132,729	117,409
Accumulated Depreciation	(61,400)	(59,892)
Net Book Value	$ 71,329	$ 57,517

Fixed Assets - Narrative (Detai

Fixed Assets - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 24,598	$ 25,133	$ 27,111

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Beginning Balance	$ 731,691	$ 732,752
Acquired goodwill	0	1,025
Impairment loss recognized	(61,661)	(4,879)
Transfer of goodwill between segments	0	0
Disposition	(7,074)
Foreign currency translation	5,255	2,793
Ending Balance	668,211	731,691
Integrated Networks - Group A
Goodwill [Roll Forward]
Beginning Balance	134,573	139,452
Acquired goodwill	0	0
Impairment loss recognized	0	(4,879)
Transfer of goodwill between segments	0	0
Disposition	0
Foreign currency translation	0	0
Ending Balance	134,573	134,573
Integrated Networks - Group B
Goodwill [Roll Forward]
Beginning Balance	268,387	267,059
Acquired goodwill	0	1,025
Impairment loss recognized	(16,137)	0
Transfer of goodwill between segments	19,696	(120)
Disposition	0
Foreign currency translation	212	423
Ending Balance	272,158	268,387
Media & Data Network
Goodwill [Roll Forward]
Beginning Balance	105,597	101,768
Acquired goodwill	0	0
Impairment loss recognized	(5,287)	0
Transfer of goodwill between segments	4,546	3,612
Disposition	0
Foreign currency translation	538	217
Ending Balance	105,394	105,597
All Other [Domain]
Goodwill [Roll Forward]
Beginning Balance	223,134	224,473
Acquired goodwill	0	0
Impairment loss recognized	(40,237)	0
Transfer of goodwill between segments	(24,242)	(3,492)
Disposition	(7,074)
Foreign currency translation	4,505	2,153
Ending Balance	$ 156,086	$ 223,134

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Intangibles:
Trademarks (indefinite life)	$ 0	$ 14,600
Intangible assets, gross	85,305	101,506
Less accumulated amortization	(51,461)	(46,613)
Total intangible assets-net	33,844	54,893
Other Intangible Assets
Intangibles:
Intangible assets, gross	32,711	28,695
Less accumulated amortization	(18,794)	(13,942)
Intangible assets, net	13,917	14,753
Customer Relationships
Intangibles:
Intangible assets, gross	52,594	58,211
Less accumulated amortization	(32,667)	(32,671)
Intangible assets, net	$ 19,927	$ 25,540

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Textual (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)reportable_segment	Dec. 31, 2018USD ($)reportable_segment
Goodwill [Line Items]
Impairment and other losses	$ 77,240	$ 6,655	$ 96,399	$ 8,599	$ 87,204
Goodwill, Impairment Loss			61,661	4,879
Goodwill	668,211	731,691	668,211	731,691	732,752
Goodwill, impaired, accumulated impairment loss	238,965	177,304	$ 238,965	177,304
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			8 years
Amortization Of Intangible Assets, Finite Lived			$ 11,260	11,828	17,290
Indefinite-Lived Trademarks	0	14,600	$ 0	14,600
Customer Relationships
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			8 years
Trademarks
Goodwill [Line Items]
Impairment of Intangible Assets (Excluding Goodwill)	$ 12,071
Finite-Lived Intangible Asset, Useful Life	5 years
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			9 years
Indefinite-Lived Trademarks	$ 14,600		$ 14,600
Integrated Networks - Group A
Goodwill [Line Items]
Goodwill, Impairment Loss			0	4,879
Goodwill	134,573	134,573	134,573	134,573	139,452
Integrated Networks - Group A | Reporting Unit, 1 [Member]
Goodwill [Line Items]
Goodwill	14,854		14,854
Integrated Networks - Group B
Goodwill [Line Items]
Goodwill, Impairment Loss			16,137	0
Goodwill	272,158	268,387	272,158	$ 268,387	$ 267,059
Media & Data Network
Goodwill [Line Items]
Number of Reporting Units | reportable_segment				1	1
Goodwill, Impairment Loss			5,287	$ 0
Goodwill	105,394	$ 105,597	105,394	$ 105,597	$ 101,768
All Other | Reporting Unit, 2 [Member]
Goodwill [Line Items]
Goodwill	$ 5,479		$ 5,479

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Schedule of Finite-lived Intangible Assets Amortization Expense (Details) $ in Thousands	Dec. 31, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2021	$ 8,514
2022	8,062
2023	7,711
2024	4,558
Thereafter	$ 4,999

Deferred Acquisition Consider_3

Deferred Acquisition Consideration (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			$ 74,671	$ 82,598
Payments			46,792	30,719
Redemption value adjustments			44,993	15,451
Additions			7,703	7,145
Foreign translation adjustment			2,227	196
Ending balance of contingent payments	$ 82,802	$ 74,671	82,802	74,671
Deferred acquisition consideration	83,065	75,220	83,065	75,220
Loss attributable to fair value adjustments	41,672	9,030
Stock-based compensation			2,806	10,048
Fixed payments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deferred acquisition consideration	$ 263	$ 549	263	549
Contingent Payment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Loss attributable to fair value adjustments			$ 42,187	$ 5,403

Leases - Lease Costs and Other

Leases - Lease Costs and Other Quantitative Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease cost	$ 71,257	$ 67,044	$ 65,093
Variable lease cost	14,640	18,879
Sublease rental income	(11,329)	(8,965)	$ (3,671)
Total lease cost	74,568	76,958
Operating cash flows	70,277	69,735
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 45,663	$ 269,801
Weighted average remaining lease term (in years) - Operating leases	7 years 2 months 12 days	5 years 3 months 18 days
Weighted average discount rate - Operating leases	10.60%	8.60%

Leases - Minimum Future Rental

Leases - Minimum Future Rental Payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Leases [Abstract]
2021	$ 68,375
2022	60,252
2023	56,842
2024	49,909
2025	38,880
2026 and thereafter	150,950
Total	425,208
Less: Present value discount	(136,757)
Lease liability	$ 288,451

Leases - Additional Information

Leases - Additional Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)lease	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Lessee, Lease, Description [Line Items]
Number of leases not yet commenced | lease	3
Leases not yet commenced, liability		$ 25,900
Operating lease charge	$ 22,667
Impairment of right-of-use asset	9,969	3,700
Operating lease cost	71,257	67,044	$ 65,093
Sublease rental income	$ 11,329	$ 8,965	$ 3,671

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt [Line Items]
Revolving credit agreement	$ 0	$ 0
Debt issuance costs	$ (27,072)	(12,370)
6.50% Notes due 2024
Debt [Line Items]
Senior Notes		$ 900,000

Debt (Details Textual)

Debt (Details Textual)	May 29, 2020USD ($)	May 28, 2020USD ($)	Apr. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Mar. 11, 2021
Debt [Line Items]
Interest Expense, Debt				$ 59,147,000	$ 62,210,000	$ 64,420,000
Amortization of Debt Issuance Costs and Discounts				$ 3,529,000	3,346,000	$ 3,193,000
6.50% Notes due 2024
Debt [Line Items]
Senior Notes					900,000,000
Interest rate, stated percentage				7.50%
Debt Instrument, Repurchased Face Amount			$ 29,744,000
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed			73.90%
Interest Payable			$ 946,000
Debt Instrument, Repurchase Amount			21,999,000
Gain (Loss) on Extinguishment of Debt			$ 7,388,000
Consent fee accrued				$ 17,400,000
Consent fee (percent)				2.00%
Long-term Debt, Maturities, Repayments of Principal in Year Four				$ 870,256,000
Senior Notes | 6.50% Notes due 2024
Debt [Line Items]
Debt Instrument, Percentage Of Redemption Price, Change In Ownership Control				101.00%
Debt Instrument, Percentage Of Redemption Price, Redemption Date, Latest For Redemption At Face Amount				100.00%
Line of Credit [Member]
Debt [Line Items]
Maximum borrowing capacity	$ 211,500	$ 250,000		$ 211,500,000
Long-term Line of Credit				$ 0	0
Debt Instrument, Covenant, Earnings Before Interest, Taxes and Depreciation and Amortization	$ 120,000,000	$ 105,000,000
Ratio of Indebtedness to Net Capital				6.25
Letter of Credit [Member]
Debt [Line Items]
Maximum borrowing capacity				$ 18,651,000	$ 4,836,000
Subsequent Event [Member] | Line of Credit [Member]
Debt [Line Items]
Ratio of Indebtedness to Net Capital							5.5
Non-prime Rate [Member] | Line of Credit [Member] | Minimum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
Non-prime Rate [Member] | Line of Credit [Member] | Maximum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
Prime Rate [Member] | Line of Credit [Member] | Minimum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	1.75%
Prime Rate [Member] | Line of Credit [Member] | Maximum
Debt [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.25%

Employee Benefit Plans - Schedu

Employee Benefit Plans - Schedule of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost on benefit obligation	1,426	1,640	1,641
Expected return on plan assets	(1,924)	(1,604)	(1,948)
Curtailment and settlements	2,333	626	1,039
Amortization of actuarial losses	340	266	258
Net periodic benefit cost	$ 2,175	$ 928	$ 990

Employee Benefit Plans - Sche_2

Employee Benefit Plans - Schedule of Assumptions Used to Determine Net Periodic Costs (Details)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.39%	4.42%	3.83%
Expected return on plan assets	7.00%	7.00%	7.00%

Employee Benefit Plans - Sche_3

Employee Benefit Plans - Schedule of Defined Benefit Plan Amounts in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Current year actuarial (gain) loss	$ 2,213	$ 2,917	$ (520)
Amortization of actuarial loss	(340)	(266)	(258)
Total recognized in other comprehensive (income) loss	1,873	2,651	(778)
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ 4,048	$ 3,579	$ 212

Employee Benefit Plans - Sche_4

Employee Benefit Plans - Schedule of Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligation:
Benefit obligation, Beginning balance	$ 43,012	$ 37,938	$ 43,750
Interest Cost	1,426	1,640	1,641
Actuarial (gains) losses	5,301	6,127	(3,522)
Benefits paid	(6,728)	(2,693)	(3,931)
Benefit obligation, Ending balance	43,011	43,012	37,938
Change in plan assets:
Fair value of plan assets, Beginning balance	27,206	23,181	27,977
Actual return on plan assets	2,678	4,188	(2,093)
Employer contributions	2,325	2,530	1,228
Benefits paid	(6,728)	(2,693)	(3,931)
Fair value of plan assets, Ending balance	25,481	27,206	23,181
Unfunded status	$ 17,530	$ 15,806	$ 14,757

Employee Benefit Plans - Sche_5

Employee Benefit Plans - Schedule of Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Amounts recognized in the balance sheet consist of:
Non-current liability	$ 17,530	$ 15,806	$ 14,757
Net amount recognized	$ 17,530	$ 15,806

Employee Benefit Plans - Sche_6

Employee Benefit Plans - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Accumulated net actuarial losses	$ 17,403	$ 15,530
Amount recognized	$ 17,403	$ 15,530

Employee Benefit Plans - Sche_7

Employee Benefit Plans - Schedule of Assumptions Used to Determine Benefit Obligation (Details)	Dec. 31, 2020	Dec. 31, 2019
Retirement Benefits [Abstract]
Discount rate	2.55%	3.39%

Employee Benefit Plans - Sche_8

Employee Benefit Plans - Schedule of Changes in Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 25,481	$ 27,206	$ 23,181	$ 27,977
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,442	25,931
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,039	1,275
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,481	27,206
Fair Value, Inputs, Level 1 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	24,442	25,931
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,039	1,275
Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 2 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 3 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Employee Benefit Plans - Sche_9

Employee Benefit Plans - Schedule of Allocation of Plan Assets (Details)	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Target allocation	100.00%
Actual allocation	100.00%	100.00%
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target allocation	5.00%
Actual allocation	4.00%	4.70%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	65.00%
Actual allocation	69.00%	66.70%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	30.00%
Actual allocation	27.00%	28.60%

Employee Benefit Plans - Sch_10

Employee Benefit Plans - Schedule of Expected Benefit Payments (Details) $ in Thousands	Dec. 31, 2020USD ($)
Estimated Future Benefit Payments for FYE 12/31
2021	$ 1,802
2022	1,769
2023	1,983
2024	2,231
2025	2,171
Thereafter	$ 10,796

Employee Benefit Plans - Textua

Employee Benefit Plans - Textual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Estimate of net actuarial losses reclassified from AOCI in the next fiscal year		$ (1,354)	$ (1,911)
Current employer pension plan contributions		2,325	$ 2,530	$ 1,228
Forecast | Reclassification out of Accumulated Other Comprehensive Income
Defined Benefit Plan Disclosure [Line Items]
Estimate of net actuarial losses reclassified from AOCI in the next fiscal year	$ 413
Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Expected pension plan contribution		$ 2,415

Noncontrolling and Redeemable_3

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Amounts Due to Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Beginning balance	$ 14,028	$ 9,278
Income attributable to noncontrolling interests	21,774	16,156	$ 11,785
Distributions made	(15,192)	(11,392)
Other	94	(14)
Ending balance	$ 20,704	$ 14,028	$ 9,278

Noncontrolling and Redeemable_4

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.	$ (233,457)	$ 4,076	$ (593)	$ 1,003	$ (7,678)	$ (1,752)	$ 4,290	$ (113)	$ (228,971)	$ (5,253)	$ (130,007)
Business acquisitions and step-up transactions, net of tax									1,626	1,911	25,550
Change from net loss attributable to MDC Partners Inc. and transfers to noncontrolling interests									227,345	3,342	119,867
MDC Partners Inc. Shareholders' Deficit
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.										(5,253)	(130,007)
Business acquisitions and step-up transactions, net of tax									$ 1,626	$ 1,911	$ 10,140

Noncontrolling and Redeemable_5

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Noncontrolling Interest [Abstract]
Beginning Balance	$ 36,973	$ 51,546
Redemptions	(12,289)	(14,530)
Granted	0	0
Changes in redemption value	2,800	(3,163)
Currency translation adjustments	(347)	3
Other	0	3,117
Ending Balance	$ 27,137	$ 36,973

Noncontrolling and Redeemable_6

Noncontrolling and Redeemable Noncontrolling Interests (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 27,137	$ 36,973	$ 51,546
Vesting over period [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	17,184
Termination, disability, or death [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	9,953
Acquisition Value in excess of Redemption Value [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 0

Commitments, Contingencies an_2

Commitments, Contingencies and Guarantees (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Letter of Credit [Member]
Other Commitments [Line Items]
Maximum borrowing capacity	$ 18,651	$ 4,836

Share Capital - Textual (Detail

Share Capital - Textual (Details)	Mar. 14, 2019USD ($)$ / sharesshares	Mar. 07, 2017USD ($)$ / sharesshares	Dec. 31, 2020USD ($)vote$ / sharesshares	Dec. 31, 2019USD ($)vote$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017shares
Share Capital [Line Items]
Proceeds from issuance of common and convertible preference shares, net of issuance costs			$ 0	$ 98,620,000	$ 0
Issuance of common and convertible preference shares				98,620,000
Convertible preference shares, 145,000 authorized, issued and outstanding at December 31, 2020 and 2019			152,746,000	152,746,000
Expenses for convertible preference shares					(97,000)
Share-based Payment Arrangement, Expense			5,774,000	2,460,000	5,892,000
Share-based Payment Arrangement, Expense, Tax Benefit			$ 0	643,000	472,000
Convertible Preference Shares
Share Capital [Line Items]
Proceeds from issuance of common and convertible preference shares, net of issuance costs	$ 98,620,000
Issuance of common and convertible preference shares				$ 62,623,000
Expenses for convertible preference shares					$ (97,000)
Convertible Preference Shares | Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Issuance of common and convertible preference shares (in shares) | shares		95,000
Sale of Stock, Issuance Authorized		$ 95,000,000
Proceeds from issuance of common and convertible preference shares, net of issuance costs		$ 90,123,000
Preferred Stock, Liquidation Preference Per Share | $ / shares		$ 1,000
Preferred Stock, Conversion Price per Voting Share | $ / shares	$ 7.42	$ 10
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Accretion Rate, Preference Per Share | $ / shares			$ 8.84	$ 8.17
Preferred Stock, Accretion of Redemption Discount			$ 9,789,000	$ 9,043,000
Preferred Stock, Liquidation Preference, Value			$ 128,539,000
Shares outstanding (shares) | shares			145,000,000	145,000,000	95,000,000	95,000,000
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%
Convertible Preference Shares | Series 6 Convertible Preferred Shares [Member]
Share Capital [Line Items]
Issuance of common and convertible preference shares (in shares) | shares	50,000,000
Proceeds from Issuance or Sale of Equity	$ 62,623,000
Proceeds from issuance of common and convertible preference shares, net of issuance costs	$ 50,000,000
Preferred Stock, Liquidation Preference Per Share | $ / shares	$ 1,000
Preferred Stock, Conversion Price per Voting Share | $ / shares	$ 5
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Convertible Preference Shares, Accretion Period	5 years
Preferred Stock, Monthly Accretion of Redemption Discount			$ 7.54	$ 6.96
Preferred Stock, Accretion of Redemption Discount			4,390,000	3,261,000
Preferred Stock, Liquidation Preference, Value			$ 57,651,000
Preferred Stock, Convertible Preference Shares, Convertible at Company's Option, Term	2 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]
Issuance of common and convertible preference shares				$ 35,997,000
Common Shares | Common Class A
Share Capital [Line Items]
Issuance of common and convertible preference shares (in shares) | shares	14,285,714
Proceeds from Issuance of Common Stock	$ 50,000,000
Proceeds from Issuance or Sale of Equity	$ 35,997,000
Shares outstanding (shares) | shares			73,529,105	72,150,854
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	3,749	3,755
Common stock, voting rights, number of votes per share | vote				20
Employee Stock Incentive Plan [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | shares			18,150,000
Deferred Compensation Arrangement with Individual, Common Stock Reserved for Future Issuance | shares			5,108,583
Share-based Payment Arrangement, Option [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Option, Nonvested, Weighted Average Exercise Price | $ / shares			$ 0	$ 2.23	$ 2.23
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term					4 years 10 months 24 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate					2.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate					52.90%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate					0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period					3 years
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period					5 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period | shares			111,866		0
Restricted Stock And Restricted Stock Units [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value			$ 5,138,000	$ 4,517,000	$ 3,583,000
Stock Appreciation Rights (SARs) [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares			$ 1.19	$ 1.14
Weighted average grant date fair value, granted (in dollars per share) | $ / shares			$ 0
Granted (in shares) | shares			0		0
Exercises (in shares) | shares			0	0	0
Vested (in shares) | shares				0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Exercisable, Number | shares			775,800
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms			9 months 18 days
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount			$ 402,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition			9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term			5 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate				0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period | shares			250,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding			$ 480,000
Performance Shares [Member] | Share-based Payment Arrangement, Option [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares			$ 3.37	$ 3.11
Weighted average grant date fair value, granted (in dollars per share) | $ / shares			$ 2.19	$ 3.08	$ 9.17
Granted (in shares) | shares			685,369
Vested (in shares) | shares			555,226
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount			$ 3,976,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition				1 year 9 months 25 days
Performance Shares [Member] | Restricted Stock And Restricted Stock Units [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms			1 year 9 months 25 days
Time Based Awards [Member] | Share-based Payment Arrangement, Option [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares			$ 2.29	$ 5.53
Weighted average grant date fair value, granted (in dollars per share) | $ / shares			$ 1.97	$ 2.54	$ 7.38
Granted (in shares) | shares			1,741,280
Vested (in shares) | shares			1,031,159
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount			$ 570,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition				1 year 25 days
Time Based Awards [Member] | Restricted Stock And Restricted Stock Units [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms			1 year 25 days
Minimum | Stock Appreciation Rights (SARs) [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares			$ 0.68
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term			3 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate			1.80%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate				62.50%
Maximum | Stock Appreciation Rights (SARs) [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares			$ 1.41
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term			4 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate			2.30%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate				67.10%

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Based Compensation Performance and Time Based (Details) - Share-based Payment Arrangement, Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	2,443,801
Granted (in shares)	685,369
Vested (in shares)	(555,226)
Forfeited (in shares)	(336,950)
Ending balance (in shares)	2,236,994	2,443,801
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 3.11
Weighted average grant date fair value, granted (in dollars per share)	2.19	$ 3.08	$ 9.17
Weighted average grant date fair value, vested (in dollars per share)	2.96
Weighted average grant date fair value, forfeited (in dollars per share)	3.07
Weighted average grant date fair value, ending balance (in dollars per share)	$ 3.37	$ 3.11
Time Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	568,960
Granted (in shares)	1,741,280
Vested (in shares)	(1,031,159)
Forfeited (in shares)	(141,821)
Ending balance (in shares)	1,137,260	568,960
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 5.53
Weighted average grant date fair value, granted (in dollars per share)	1.97	$ 2.54	$ 7.38
Weighted average grant date fair value, vested (in dollars per share)	3.39
Weighted average grant date fair value, forfeited (in dollars per share)	3.32
Weighted average grant date fair value, ending balance (in dollars per share)	$ 2.29	$ 5.53

Share Capital - Schedule of S_2

Share Capital - Schedule of Shared Based Compensation, Stock Options (Details) - Share-based Payment Arrangement, Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	111,866
Granted (in shares)	0
Forfeited (in shares)	(111,866)		0
Exercised (in shares)	0	0	0
Ending balance (in shares)	0	111,866
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 2.23	$ 2.23
Weighted average grant date fair value, granted (in dollars per share)	0
Weighted average grant date fair value, forfeited (in dollars per share)	2.23
Weighted average grant date fair value, exercised (in dollars per share)	0
Weighted average grant date fair value, ending balance (in dollars per share)	0	2.23	$ 2.23
Weighted average exercise price, beginning balance (in dollars per share)	4.85
Weighted average exercise price, granted (in dollars per share)	0
Weighted average exercise price, forfeited (in dollars per share)	0
Weighted average exercise price, exercised (in dollars per share)	4.85
Weighted average exercise price, ending balance (in dollars per share)	$ 0	$ 4.85

Share Capital - Schedule of S_3

Share Capital - Schedule of Share Based Compensation, Stock Appreciation Rights (Details) (Details) - Stock Appreciation Rights (SARs) [Member]	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares) | shares	2,325,800
Ending balance (in shares) | shares	2,075,800
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 1.14
Weighted average grant date fair value, ending balance (in dollars per share)	1.19
Weighted average exercise price, beginning balance (in dollars per share)	3.07
Weighted average exercise price, ending balance (in dollars per share)	2.84
Weighted average grant date fair value, granted (in dollars per share)	0
Weighted average exercise price, vested (in dollars per share)	$ 0
Granted (in shares) | shares	0
Exercised (in shares) | shares	0
Weighted average grant date fair value, forfeited (in dollars per share)	$ 0.73
Weighted average exercise price, exercised (in dollars per share)	$ 5
Forfeited (in shares) | shares	(250,000)
Weighted average exercise price, forfeited (in dollars per share)	$ 0

Changes in Accumulated Other _3

Changes in Accumulated Other Comprehensive Income - Schedule of Changes in AOCI(L) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Defined benefit pension, balance January 1	$ (15,012)	$ (13,101)
Foreign currency translation, balance January 1	10,743	17,821
Total, balance January 1	(4,269)	4,720
Other comprehensive income (loss) before reclassifications, defined benefit plan	0	0
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Gain (Loss), before Reclassification and Tax	8,362	(7,078)
Total, other comprehensive income (loss) before reclassifications	8,362	(7,078)
Amounts reclassified from accumulated other comprehensive income (loss)	(1,354)	(1,911)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Total, amounts reclassified from accumulated other comprehensive income (loss)	(1,354)	(1,911)
Defined benefit pension, other comprehensive income (loss)	(1,354)	(1,911)	$ 555
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent	8,362	(7,078)
Total, other comprehensive income (loss)	7,008	(8,989)
Defined benefit pension, balance December 31	(16,366)	(15,012)	(13,101)
Foreign currency translation, balance December 31	19,105	10,743	17,821
Total, balance December 31	$ 2,739	$ (4,269)	$ 4,720

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income before income tax, Domestic and Foreign (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	$ (88,402)	$ 20,867	$ (88,669)
Domestic Tax Authority
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	(73,227)	(17,491)	(76,960)
Non-U.S.
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	$ (15,175)	$ 38,358	$ (11,709)

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax [Line Items]
Current tax provision	$ 7,999	$ 5,525	$ 8,030
Deferred tax provision (benefit)	108,556	4,791	21,585
Income tax provision (benefit)	116,555	10,316	29,615
United States Federal
Income Tax [Line Items]
Current tax provision	3,016	2,638	444
Deferred tax provision (benefit)	75,686	4,635	(10,817)
United States And Local
Income Tax [Line Items]
Current tax provision	742	12	2
Deferred tax provision (benefit)	34,404	1,130	(3,476)
Foreign
Income Tax [Line Items]
Current tax provision	4,241	2,875	7,584
Deferred tax provision (benefit)	$ (1,534)	$ (974)	$ 35,878

Income Taxes - Schedule of Effe

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest	$ (88,402)	$ 20,867	$ (88,669)
Tax expense (benefit) using U.S. statutory income tax rate	(18,564)	4,382	(18,621)
State and foreign taxes	(3,486)	1,496	(3,944)
Non-deductible stock-based compensation	1,162	3,823	1,512
Global intangible low-taxed income	1,363	1,147	710
Base erosion and anti-abuse tax	4,697	2,504	389
Other non-deductible expense	1,043	273	1,388
Change to valuation allowance	128,938	(2,830)	49,482
Effect of the difference in U.S. federal and local statutory rates	67	1,422	(152)
Noncontrolling interests	(4,649)	(3,566)	(2,674)
Impact of foreign operations	1,160	2,724	612
Impact of goodwill impairments	10,158	436	8,703
Adjustments to accrued taxes in previous periods	4,641	(3,544)	1,192
Adjustment to deferred tax balances	(9,999)	1,920	(8,845)
Other, net	24	129	(137)
Income tax provision (benefit)	$ 116,555	$ 10,316	$ 29,615
Effective income tax rate	(131.80%)	49.40%	(33.40%)

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Capital assets and other	$ 20,831	$ 10,987
Net operating loss carry forwards	47,139	60,705
Interest deductions	20,819	16,797
Refinancing charge	0	669
Goodwill and intangibles	122,045	117,421
Stock compensation	1,693	1,736
Pension plan	4,856	4,414
Unrealized foreign exchange	11,995	11,373
Capital loss carry forwards	13,657	13,081
Accounting reserves	77,870	76,397
Gross deferred tax asset	320,905	313,580
Less: valuation allowance	(198,452)	(65,649)
Net deferred tax assets	122,453	247,931
Deferred tax liabilities:
Right-of-use assets	(57,890)	(67,613)
Refinancing charge	(1,675)	0
Withholding taxes	(475)	(546)
Capital assets	(1,893)	(382)
Goodwill amortization	(88,326)	(98,677)
Total deferred tax liabilities	(150,259)	(167,218)
Net deferred tax asset (liability)	(27,806)
Net deferred tax asset (liability)		80,713
Disclosed as:
Deferred tax assets	179	84,900
Deferred tax liabilities	$ (27,985)	$ (4,187)

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in Tax Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Reserve [Roll Forward]
Beginning Balance	$ 996	$ 887	$ 1,433
Current year positions	581	275	0
Prior period positions	0	0	7
Settlements	0	0	(314)
Lapse of statute of limitations	(170)	(166)	(239)
Ending Balance	$ 1,407	$ 996	$ 887

Income Taxes - Textual (Details

Income Taxes - Textual (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax [Line Items]
Income tax expense (benefit)	$ 116,555,000	$ 10,316,000	$ 29,615,000
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest	(88,402,000)	20,867,000	(88,669,000)
Income taxes receivable	1,480,000	5,025,000
Taxes payable	9,238,000	11,722,000
Operating loss carryforwards	229,224,000
Indefinite loss carryforwards	122,299,000
Tax credit carryforwards	5,460,000
Valuation allowance	198,452,000	65,649,000
Valuation allowance, deferred tax asset, increase (decrease), amount	(129,000,000)
Tax expense related to estimated tax costs associated with change in assertion	475,000	546,000
Undistributed earnings no longer subject to reinvestment assertion	4,745,000	5,462,000
Unrecognized tax benefits	1,066,000	1,107,000
Unrecognized tax benefits, income tax penalties and interest accrued	135,000	111,000
Unrecognized tax benefits, reduction to deferred tax asset	477,000
United States
Income Tax [Line Items]
Operating loss carryforwards	1,533,000
Indefinite loss carryforwards	42,003,000
State and Local Jurisdiction
Income Tax [Line Items]
Operating loss carryforwards	132,655,000
Indefinite loss carryforwards	69,967,000
Non-U.S.
Income Tax [Line Items]
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest	(15,175,000)	$ 38,358,000	$ (11,709,000)
Operating loss carryforwards	95,036,000
Indefinite loss carryforwards	10,329,000
Canada
Income Tax [Line Items]
Indefinite loss carryforwards	103,074,000
Minimum
Income Tax [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	400,000
Maximum
Income Tax [Line Items]
Decrease in unrecognized tax benefits is reasonably possible	$ 500,000

Fair Value Measurements (Detail

Fair Value Measurements (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Goodwill, Impairment Loss			$ 61,661	$ 4,879
Impairment and other losses	$ 77,240	$ 6,655	96,399	8,599	$ 87,204
Operating lease charge			22,667
Impairment of right-of-use asset			9,969	3,700
Variable lease cost			14,640	18,879
Lessee, Lease Property in New York [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Variable lease cost			$ 12,698
Measurement Input, Discount Rate [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Business Combination, Contingent Consideration, Liability, Measurement Input	0.051		0.051
Senior Notes | Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ 870,256	900,000	$ 870,256	900,000
Senior Notes | Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Debt Instrument, Fair Value Disclosure	$ 883,580	$ 812,250	$ 883,580	$ 812,250

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	3 Months Ended	5 Months Ended	12 Months Ended			15 Months Ended
	Oct. 31, 2020	Mar. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Related Party Transaction [Line Items]
Sublease rental income			$ 11,329	$ 8,965	$ 3,671
Stagwell Subsidiary [Member] | Services Provided By Subisidiary [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction						$ 2,000
Due to Related Parties			1,200			1,200
Stagwell Subsidiary [Member] | Media Planning, Buying and Reporting [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction			56,700
Due from Related Parties			110			110
Stagwell Subsidiary [Member] | Development of Advertising Technology [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction			483
Due to Related Parties			2			2
Stagwell Subsidiary [Member] | Audience and Brand Research, Concept Testing and Landscape [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction	$ 145
Due to Related Parties			63			63
Stagwell Subsidiary [Member] | Event Management Services [Member]
Related Party Transaction [Line Items]
Due from Related Parties			$ 67			$ 67
Forecast | Stagwell Subsidiary [Member] | Event Management Services [Member]
Related Party Transaction [Line Items]
Related Party Transaction, Amounts of Transaction		$ 457

Segment Information (Details 1)

Segment Information (Details 1) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)reportable_segment	Dec. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment										3
Revenue	$ 328,168	$ 283,423	$ 259,678	$ 327,742	$ 381,975	$ 342,907	$ 362,130	$ 328,791	$ 1,199,011	$ 1,415,803	$ 1,475,088
Adjusted EBITDA									177,332	174,153	161,451
Depreciation and amortization									(36,905)	(38,329)	(46,196)
Goodwill and other asset impairment	(77,240)				(6,655)				(96,399)	(8,599)	(87,204)
Stock-based compensation	(3,611)				(18,408)				(14,179)	(31,040)	(18,416)
Deferred acquisition consideration expense/(income)									(42,187)	(5,403)	457
Loss on investments									(2,175)	(2,048)	(779)
Other expense									(31,244)	(9,274)	(7,879)
Segment operating income (loss)									(45,757)	79,460	1,434
Interest expense and finance charges									(62,163)	(64,942)	(67,075)
Foreign exchange gain (loss)	6,274				4,349				(982)	8,750	(23,258)
Other, net									20,500	(2,401)	230
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates									(88,402)	20,867	(88,669)
Income tax expense									116,555	10,316	29,615
Income (loss) before equity in earnings of non-consolidated affiliates									(204,957)	10,551	(118,284)
Equity in earnings of non-consolidated affiliates									(2,240)	352	62
Net income (loss)									(207,197)	10,903	(118,222)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(226,303)	14,804	2,508	1,794	(2,259)	5,513	7,333	316
Net income attributable to the noncontrolling interest									(21,774)	(16,156)	(11,785)
Net income (loss) attributable to MDC Partners Inc.	$ (233,457)	$ 4,076	$ (593)	$ 1,003	$ (7,678)	$ (1,752)	$ 4,290	$ (113)	(228,971)	(5,253)	(130,007)
Capital expenditures									37,303	18,596	20,264
Capital Expenditures Incurred but Not yet Paid									12,993
Integrated Networks - Group A
Segment Reporting Information [Line Items]
Revenue									379,648	392,101	393,890
Adjusted EBITDA									79,793	74,822	75,609
Depreciation and amortization									(6,467)	(8,559)	(9,602)
Stock-based compensation									(7,580)	(24,420)	(5,792)
Capital expenditures									1,087	5,934	8,228
Integrated Networks - Group B
Segment Reporting Information [Line Items]
Revenue									435,589	531,717	551,317
Adjusted EBITDA									84,297	84,568	74,091
Depreciation and amortization									(17,204)	(15,904)	(19,032)
Stock-based compensation									(3,191)	(4,303)	(6,890)
Capital expenditures									987	9,270	6,352
Media & Data Network
Segment Reporting Information [Line Items]
Revenue									139,015	161,451	183,287
Adjusted EBITDA									9,707	7,746	12,205
Depreciation and amortization									(4,376)	(4,303)	(3,820)
Stock-based compensation									(122)	(63)	(320)
Capital expenditures									569	627	1,632
All Other
Segment Reporting Information [Line Items]
Revenue									244,759	330,534	346,594
Adjusted EBITDA									30,755	37,618	38,307
Depreciation and amortization									(7,478)	(8,695)	(12,980)
Stock-based compensation									(304)	(374)	(755)
Capital expenditures									966	2,729	3,985
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Adjusted EBITDA									(27,220)	(30,601)	(38,761)
Depreciation and amortization									(1,380)	(868)	(762)
Stock-based compensation									(2,982)	(1,880)	(4,659)
Capital expenditures									$ 33,694	$ 36	$ 67

Segment Information - Schedule

Segment Information - Schedule of Fixed Assets, Goodwill and Intangibles, Net (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Fixed assets, net book value	$ 90,413				$ 81,054				$ 90,413	$ 81,054
Intangible Assets, Net (Including Goodwill)	702,055				786,584				702,055	786,584
Services	328,168	$ 283,423	$ 259,678	$ 327,742	381,975	$ 342,907	$ 362,130	$ 328,791	1,199,011	1,415,803	$ 1,475,088
UNITED STATES
Segment Reporting Information [Line Items]
Fixed assets, net book value	80,447				68,497				80,447	68,497
Intangible Assets, Net (Including Goodwill)	614,168				659,584				614,168	659,584
Services									959,636	1,116,045	1,152,399
CANADA
Segment Reporting Information [Line Items]
Fixed assets, net book value	3,461				4,475				3,461	4,475
Intangible Assets, Net (Including Goodwill)	51,267				64,842				51,267	64,842
Services									81,930	105,067	124,001
Other
Segment Reporting Information [Line Items]
Fixed assets, net book value	6,505				8,082				6,505	8,082
Intangible Assets, Net (Including Goodwill)	$ 36,620				$ 62,158				36,620	62,158
Services									$ 157,445	$ 194,691	$ 198,688

Quarterly Results of Operatio_3

Quarterly Results of Operations - Schedule of Results of Operations (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 328,168	$ 283,423	$ 259,678	$ 327,742	$ 381,975	$ 342,907	$ 362,130	$ 328,791	$ 1,199,011	$ 1,415,803	$ 1,475,088
Cost of services sold	209,043	172,531	165,632	222,693	260,725	222,448	240,749	237,154	769,899	961,076	991,198
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(226,303)	14,804	2,508	1,794	(2,259)	5,513	7,333	316
Net loss attributable to MDC Partners Inc.	$ (233,457)	$ 4,076	$ (593)	$ 1,003	$ (7,678)	$ (1,752)	$ 4,290	$ (113)	$ (228,971)	$ (5,253)	$ (130,007)
Earnings Per Share, Basic	$ (3.23)	$ (0.07)	$ (0.06)	$ (0.03)	$ (0.15)	$ (0.07)	$ 0.01	$ (0.04)
Earnings Per Share, Diluted	$ (3.23)	$ (0.07)	$ (0.06)	$ (0.03)	$ (0.15)	$ (0.07)	$ 0.01	$ (0.04)

Quarterly Results of Operatio_4

Quarterly Results of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition, Contingent Consideration [Line Items]
Foreign exchange gain (loss)	$ 6,274	$ 4,349	$ (982)	$ 8,750	$ (23,258)
Stock-based compensation	3,611	18,408	14,179	31,040	18,416
Loss attributable to fair value adjustments	41,672	9,030
Impairment and other losses	$ 77,240	$ 6,655	96,399	8,599	$ 87,204
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount			129,000
Contingent Payment
Business Acquisition, Contingent Consideration [Line Items]
Loss attributable to fair value adjustments			$ 42,187	$ 5,403

SEC Schedule, Article 12-09, Va

SEC Schedule, Article 12-09, Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 3,304	$ 1,879	$ 2,453
Charged to Costs and Expenses	3,487	2,996	1,538
Removal of Uncollectible Receivables	(1,305)	(1,377)	(1,795)
Translation Adjustments Increase (Decrease)	(13)	(194)	(317)
Balance at the End of Period	5,473	3,304	1,879
Valuation allowance for deferred income taxes
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	65,649	68,479	19,032
Charged to Costs and Expenses	128,938	(2,830)	49,447
Other	2,436	0	0
Translation Adjustments Increase (Decrease)	1,429	0	0
Balance at the End of Period	$ 198,452	$ 65,649	$ 68,479