Stagwell (STGW) 10-K 5 Mar 20 2019 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Feb. 21, 2020	Jun. 28, 2019	Dec. 31, 2018	Dec. 31, 2017
Document Information [Line Items]
Trading Symbol	MDCA
Entity Registrant Name	MDC PARTNERS INC
Entity Central Index Key	0000876883
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Current Reporting Status	Yes
Document Type	10-K
Entity Small Business	true
Document Fiscal Year Focus	2019
Document Period End Date	Dec. 31, 2019
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Public Float			$ 140.7
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		72,166,854
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,749
Common Shares | Common Class A
Document Information [Line Items]
Shares outstanding (shares)	72,150,854			57,517,568
Common Shares | Common Class B
Document Information [Line Items]
Shares outstanding (shares)	3,749			3,755	3,755

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Services	$ 1,415,803	$ 1,476,203	$ 1,513,779
Operating expenses:
Cost of services sold	961,076	991,198	1,023,476
Office and general expenses	328,339	349,056	310,455
Depreciation and amortization	38,329	46,196	43,474
Goodwill and other asset impairment	7,819	80,057	4,415
Costs and Expenses, Total	1,335,563	1,466,507	1,381,820
Operating income	80,240	9,696	131,959
Other income (expense):
Interest expense and finance charges, net	(64,942)	(67,075)
Interest Expense, Other			64,364
Other, net	(2,401)	230	1,346
Foreign exchange gain (loss)	8,750	(23,258)	18,137
Nonoperating Income (Expense), Total	(58,593)	(90,103)	(44,881)
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	21,647	(80,407)	87,078
Income tax expense (benefit)	10,533	31,603	(168,064)
Income (loss) before equity in earnings of non-consolidated affiliates	11,114	(112,010)	255,142
Equity in earnings of non-consolidated affiliates	352	62	2,081
Net income (loss)	11,466	(111,948)	257,223
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest			257,223
Net income attributable to the noncontrolling interest	(16,156)	(11,785)	(15,375)
Net income (loss) attributable to MDC Partners Inc.	(4,690)	(123,733)	241,848
Net income (loss) attributable to MDC Partners Inc. common shareholders	$ (16,994)	$ (132,088)	$ 205,594
Basic and diluted
Earnings per share, basic	$ (0.25)	$ (2.31)	$ 3.72
Earnings per share, diluted	$ (0.25)	$ (2.31)	$ 3.71
Weighted Average Number of Common Shares Outstanding:
Weighted Average Number of Shares Outstanding, Basic	69,132,100	57,218,994	55,255,797
Weighted Average Number of Shares Outstanding, Diluted	69,132,100	57,218,994	55,481,786
Stock-based compensation	$ 31,040	$ 18,416	$ 24,350
Cost of services sold
Weighted Average Number of Common Shares Outstanding:
Stock-based compensation	29,160	12,513	19,015
Office and general expenses
Weighted Average Number of Common Shares Outstanding:
Stock-based compensation	$ 1,880	5,903	5,335
Series 4 Convertible Preferred Stock [Domain] | Convertible Preference Shares
Other income (expense):
Accretion on and net income allocated to convertible preference shares		$ 8,355	$ 36,254

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (LOSS) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Comprehensive income (loss)
Net loss	$ 11,466	$ (111,948)	$ 257,223
Other comprehensive income (loss), net of applicable tax:
Foreign currency translation adjustment	(6,691)	3,158	3,611
Benefit plan adjustment, net of income tax expense (benefit) of ($740) for 2019, $223 for 2018 and nil for 2017	(1,911)	555	(1,336)
Other comprehensive income (loss)	(8,602)	3,713	2,275
Comprehensive income (loss) for the period	2,864	(108,235)	259,498
Comprehensive income attributable to the noncontrolling interests	(16,543)	(8,824)	(17,780)
Comprehensive income (loss) attributable to MDC Partners Inc.	$ (13,679)	$ (117,059)	$ 241,718

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current Assets:
Cash and cash equivalents	$ 106,933	$ 30,873
Accounts receivable, less allowance for doubtful accounts of $3,304 and $1,879	450,403	395,200
Expenditures billable to clients	30,133	42,369
Assets held for sale	0	78,913
Other current assets	35,613	42,499
Total Current Assets	623,082	589,854
Fixed assets, at cost, less accumulated depreciation of $129,579 and $128,546	81,054	88,189
Right-of-use assets - operating leases	223,622	0
Investments in non-consolidated affiliates	6,161	6,556
Goodwill	740,674	740,955
Other intangible assets, net	54,893	67,765
Deferred tax assets	85,988	92,741
Other assets	24,018	25,513
Total Assets	1,839,492	1,611,573
Current Liabilities:
Accounts payable	200,148	221,995
Accruals and other liabilities	353,575	313,141
Liabilities held for sale	0	35,967
Advance billings	171,742	138,505
Current portion of lease liabilities - operating leases	48,659	0
Current portion of deferred acquisition consideration	45,521	32,928
Total Current Liabilities	819,645	742,536
Long-term debt	887,630	954,107
Long-term portion of deferred acquisition consideration	29,699	50,767
Long-term lease liabilities - operating leases	219,163	0
Other liabilities	21,584	54,255
Deferred tax liabilities	4,187	5,329
Total Liabilities	1,981,908	1,806,994
Redeemable Noncontrolling Interests	36,973	51,546
Shareholders’ Deficit:
Convertible preference shares, 145,000 authorized, issued and outstanding at December 31, 2019 and 95,000 at December 31, 2018	152,746	90,123
Common stock and other paid-in capital	101,469	58,579
Accumulated deficit	(469,593)	(464,903)
Accumulated other comprehensive (loss) income	(4,269)	4,720
MDC Partners Inc. Shareholders' Deficit	(219,647)	(311,481)
Noncontrolling interests	40,258	64,514
Total Shareholders' Deficit	(179,389)	(246,967)
Total Liabilities, Redeemable Noncontrolling Interests and Shareholders' Deficit	$ 1,839,492	$ 1,611,573

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ 11,466	$ (111,948)	$ 257,223
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Stock-based compensation	31,040	18,416	24,350
Depreciation	25,133	27,111	23,873
Amortization of intangibles	13,196	19,085	19,601
Amortization of deferred finance charges and debt discount	3,346	3,193	3,022
Goodwill and other asset impairment	7,819	80,057	4,415
Adjustment to deferred acquisition consideration	5,403	(374)	(4,819)
Deferred income taxes (benefits)	5,008	23,573	(173,019)
(Gain) loss on disposition of assets	3,237	(1,867)	(1,600)
Earnings of non-consolidated affiliates	(352)	(62)	(2,081)
Other non-current assets and liabilities	(863)	392	(4,420)
Foreign exchange	(9,475)	20,795	(17,637)
Changes in working capital:
Accounts receivable	(37,763)	30,211	(50,030)
Expenditures billable to clients	12,236	(11,223)	1,892
Prepaid expenses and other current assets	3,474	(17,189)	6,569
Accounts payable, accruals and other current liabilities	(14,077)	(18,222)	13,398
Acquisition related payments	(5,223)	(29,141)	(42,790)
Payments For (Proceeds From) Cash In Trust	0	(656)	(709)
Advance billings	32,934	(14,871)	14,548
Net cash provided by operating activities	86,539	17,280	71,786
Cash flows from investing activities:
Capital expenditures	(18,596)	(20,264)	(32,958)
Proceeds from sale of assets	23,050	2,082	10,631
Acquisitions, net of cash acquired	(4,823)	(32,713)	0
Payments of Distributions to Affiliates	0	963	3,672
Other investments	484	(499)	(2,229)
Net cash provided by (used in) investing activities	115	(50,431)	(20,884)
Cash flows from financing activities:
Acquisition related payments	(30,155)	(32,172)	(57,083)
Distributions to noncontrolling interests	(11,392)	(13,419)	(8,865)
Payment of dividends	(56)	(196)	(284)
Purchase of shares	(601)	(776)	(1,758)
Other	0	(146)	(404)
Net cash provided by (used in) financing activities	(11,729)	21,434	(32,599)
Effect of exchange rate changes on cash, cash equivalents, and cash held in trusts	1	77	(754)
Cash, Cash Equivalents, Restricted Cash, Restricted Cash Equivalents and Cash Held in Trusts Including Cash Classified Within Assets Held for Sale, Period Increase (Decrease)	74,926	(11,640)	17,549
Change in cash and cash equivalents classified within assets held for sale	4,441	0	0
Net increase (decrease) in cash, cash equivalents, and cash held in trusts including cash classified within assets held for sale	76,060	(19,938)	17,549
Cash and cash equivalents at beginning of period	30,873	50,811	33,262
Cash and cash equivalents at end of period	106,933	30,873	50,811
Supplemental disclosures:
Cash income taxes paid	2,296	3,836	8,099
Cash interest paid	62,223	64,012	62,895
Wells Fargo Capital Finance, LLC | Revolving Credit Facility
Cash flows from financing activities:
Repayment of revolving credit facility	(1,303,350)	(1,625,862)	(1,479,632)
Proceeds from revolving credit facility	1,235,205	1,694,005	1,425,207
Change in cash and cash equivalents held in trusts classified within held for sale	(3,307)	(8,298)	0
Series 4 Convertible Preferred Stock
Cash flows from financing activities:
Proceeds from issuance of common and convertible preference shares, net of issuance costs	$ 98,620	$ 0	$ 90,220

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	Contingent Consideration, Liability Settlements [Domain]	Contingent Consideration, Liability Settlements [Domain]MDC Partners Inc. Shareholders' Deficit	Contingent Consideration, Liability Settlements [Domain]Series 4 Convertible Preferred StockConvertible Preference Shares
Balance at Dec. 31, 2016	$ (509,476)	$ 0		$ 8,563	$ (581,848)	$ (1,824)	$ (575,109)	$ 65,633
Balance (in shares) at Dec. 31, 2016										0
Common stock, balance (in shares) at Dec. 31, 2016			52,802,058
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	241,848						241,848
Other comprehensive loss	2,275					(130)	(130)	2,405
Issuance of common and convertible preference shares (in shares)		95,000,000
Issuance of common and convertible preference shares	90,220						90,220						$ 90,220
Issuance of restricted stock (in shares)			380,669
Issuance of restricted stock	0
Shares acquired and cancelled	(1,758)			(1,758)			(1,758)
Deferred acquisition consideration settled through issuance of shares (in shares)			3,353,939
Deferred acquisition consideration settled through issuance of shares	27,852			27,852			27,852
Shares acquired and cancelled (in shares)			(161,535)
Stock-based compensation	8,028			8,028			8,028
Changes in redemption value of redeemable noncontrolling interests	(1,498)			(1,498)			(1,498)
Business acquisitions and step-up transactions, net of tax	(9,650)			2,315			2,315	(11,965)
Changes in ownership interest	6,960			(5,654)			(5,654)	12,614
Dispositions	(10,657)							(10,657)
Other	343			343			343
Balance at Dec. 31, 2017	(155,513)	$ 90,220		38,191	(340,000)	(1,954)	(213,543)	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.	(123,733)						(123,733)
Other comprehensive loss	3,713					6,674	6,674	(2,961)
Expenses for convertible preference shares	(97)						(97)			$ (97)
Issuance of restricted stock (in shares)			243,529
Shares acquired and cancelled	(776)			(776)			(776)
Shares issued, acquisitions (in shares)			1,011,561
Shares issued, acquisitions									$ 7,030		$ 7,030	$ 7,030
Shares acquired and cancelled (in shares)			(108,898)
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)							(5,965)
Cumulative effect of adoption of ASC 606	(1,170)				(1,170)		(1,170)
Balance at Dec. 31, 2018	(246,967)	$ 90,123		58,579	(464,903)	4,720	(311,481)	64,514
Balance (in shares) at Dec. 31, 2018									57,517,568	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.	(4,690)				(4,690)
Other comprehensive loss	(8,602)					(8,989)	(8,989)	387
Issuance of common and convertible preference shares (in shares)		50,000,000
Issuance of common and convertible preference shares	98,620						98,620
Issuance of restricted stock (in shares)			576,932
Issuance of restricted stock	0
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)			(1,141)	(1)
Balance at Dec. 31, 2019	$ (179,389)	$ 152,746		$ 101,469	$ (469,593)	$ (4,269)	$ (219,647)	$ 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

Basis of Presentation and Recen

Basis of Presentation and Recent Developments	12 Months Ended
	Dec. 31, 2019
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”) and its subsidiaries and variable interest entities for which the Company is the primary beneficiary. References herein to “Partner Firms” generally refer to the Company’s subsidiary agencies. 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, which requires us to make judgments, assumptions and estimates that affect the amounts reported and disclosed. Actual results could differ from these estimates and assumptions. The accompanying financial statements reflect all adjustments, consisting of normally recurring accruals, which in the opinion of management are necessary for a fair presentation, in all material respects, of the information contained therein. Intercompany balances and transactions have been eliminated in consolidation. Certain reclassifications have been made to the prior year financial information to conform to the current year presentation. Due to changes in the composition of certain businesses and the Company’s internal management and reporting structure during 2019, reportable segment results for the 2018 and 2017 periods presented have been recast to reflect the reclassification of certain businesses between segments. See Note 21 of the Notes to the Consolidated Financial Statements included herein for further information. Nature of Operations MDC is a leading provider of global marketing, advertising, activation, communications and strategic consulting solutions. MDC’s Partner Firms deliver a wide range of customized services in order to drive growth and business performance for its clients. MDC Partners Inc., formerly MDC Corporation Inc., is incorporated under the laws of Canada. The Company commenced using the name MDC Partners Inc. on November 1, 2003 and legally changed its name through amalgamation with a wholly-owned subsidiary on January 1, 2004. The Company operates in North America, Europe, Asia, South America, and Australia. Recent Developments 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 purchase price of approximately $26 million , consisting of cash paid at closing plus contingent deferred payments expected to be paid over the next two years . The sale resulted in a gain estimated at approximately $16 million . An affiliate of Stagwell has a minority ownership interest in the Company. Mark Penn is the CEO and Chairman of the Board of Directors (the "Board") of the Company and is also manager of Stagwell. On February 27, 2020, in connection with the centralization of our New York real estate portfolio, the Company entered into an agreement to lease space at One World Trade Center. The lease term is for approximately eleven years commencing on April 1, 2020, with rental payments totaling approximately $115 million . As part of the centralization initiative, the Company will sublease existing properties currently under lease, resulting in the recovery of a significant portion of our rent obligation under such arrangements. 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”). Mark Penn, Chief Executive Officer and Chairman of the Company, appointed key agency executives, that report directly into him, to lead each Network. In connection with the reorganization, we are assessing a change in our reportable segments, effective with the Company’s 2020 fiscal year, to align our external reporting with how we operate the Networks under our new organizational structure.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
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 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 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 and other identifiable intangible assets. The measurement of fair value requires the use of techniques based on observable and unobservable inputs. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions. When available, the Company uses quoted market prices in active markets to determine the fair value of its financial instruments and classifies such items in Level 1. In some cases, quoted market prices are used for similar instruments in active markets and the Company classifies such items in Level 2. See Note 19 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, 2019 or December 31, 2018 . 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, 2019, 2018, or 2017. 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 ASC 842, Leases. As a result, comparative prior periods have not been adjusted and continue 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 3 and 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, are included in Investments in non-consolidated affiliates within the Consolidated Balance Sheets. 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 (cost method 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, 2019 and 2018 was $9,854 and $8,072 , 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 unless 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 and Indefinite Lived Intangibles . Goodwill (the excess of the acquisition cost over the fair value of the net assets acquired) and an indefinite life intangible asset (a trademark) acquired as a result of a business combination which are not subject to amortization are tested for impairment annually as of October 1st of each year, or more frequently if indicators of potential impairment exist. For goodwill, impairment is assessed at the reporting unit level. 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 2019 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. Indefinite-lived intangible assets are primarily evaluated on an annual basis, generally in conjunction with the Company’s evaluation of goodwill balances. 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. 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. The Company’s acquisition model typically provides for an initial payment at closing and for future additional contingent purchase price obligations. 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. Changes in such estimated values are recorded in the results of operations. 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 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 . Consistent with past practice of acquiring a majority ownership position, 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. 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 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 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. 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, 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 $11,909 , $11,136 and $10,031 for the years ended December 31, 2019 , 2018 , and 2017 , 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 (loss) income. 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, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements Adopted In The Current Reporting Period Effective January 1, 2019, the Company adopted ASC 842. As a result, comparative prior periods have not been adjusted and continue to be reported under ASC 840, Leases. With the adoption of ASC 842, the Company has elected to apply the package of practical expedients: (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. Additionally, the Company elected the practical expedient to not separate non-lease components from lease components for all operating leases. The adoption of ASC 842 had a material impact on the Company’s Consolidated Balance Sheets , resulting in the recognition, on January 1, 2019, of a lease liability of $299,243 which represents the present value of the remaining lease payments, and a right-of-use lease asset of $254,245 which represents the lease liability, offset by adjustments as appropriate under ASC 842. The adoption of ASC 842 did not have a material impact on the Company’s other Consolidated Financial Statements .

Acquisitions and Dispositions

Acquisitions and Dispositions	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions 2019 Acquisition 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 of the acquisition date, the fair value of the additional interest acquired was $6,005 . The fair value was measured using a discounted cash flow model. 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 of the acquisition date, the fair value of the additional interest acquired was $20,178 . The fair value was measured using a discounted cash flow model. 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 million in the aggregate. The sale resulted in a loss of approximately $3 million , which was included in Other, net within the Condensed Consolidated Statement of Operations. Assets and Liabilities Held for Sale - Change in Plan to Sell In the fourth quarter of 2018, the Company initiated a process to sell its ownership interest in a foreign office within the Global Integrated Agencies reportable segment. The assets and liabilities of the entity were classified as Assets and Liabilities held for sale, at their fair value less cost to sell, within the Consolidated Balance Sheet as of December 31, 2018. In the second quarter of 2019, following the appointment of Mark Penn as CEO, management changed its strategy and plan to sell the foreign office. In the second quarter of 2019, in connection with management’s decision, the amounts classified within assets and liabilities held for sale were reclassified into the respective line items within the Consolidated Balance Sheets . 2018 Acquisitions In 2018, the Company entered into various transactions in connection with certain of its majority-owned entities. These transactions were for an aggregate purchase price of $56,463 , resulting in an increase in contingent deferred consideration liabilities as of the acquisition dates of $16,174 , reduced redeemable noncontrolling interests of $9,790 , a net increase in noncontrolling interests equity of $15,411 , increased additional paid-in capital of $4,975 , and the issuance of 1,011,561 shares of the Company’s Class A subordinate voting stock. Deferred Acquisition Consideration 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 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, 2019 and December 31, 2018 . December 31, 2019 2018 Beginning balance of contingent payments $ 82,598 $ 119,086 Payments (30,719 ) (54,947 ) Redemption value adjustments (1) 15,451 3,512 Additions - acquisitions and step-up transactions 7,145 14,943 Other (2) 196 4 Ending balance of contingent payments $ 74,671 $ 82,598 Fixed payments 549 1,097 $ 75,220 $ 83,695 (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 cost of services sold and office and general expenses on the Consolidated Statements of Operations. (2) Other primarily consists of translation adjustments. The following table presents the impact to the Company’s statement of operations due to the redemption value adjustments for the contingent deferred acquisition consideration for the twelve months ended December 31, 2019 and 2018 : 2019 2018 (Income) loss attributable to fair value adjustments $ 5,403 $ (3,679 ) Stock-based compensation 10,048 7,191 Redemption value adjustments $ 15,451 $ 3,512

Revenue

Revenue	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 and 2017 : Twelve Months Ended December 31, Industry Reportable Segment 2019 2018 2017 Food & Beverage All $ 280,094 $ 313,368 $ 313,786 Retail All 148,851 152,552 178,152 Consumer Products All 167,324 162,524 162,307 Communications All 184,870 178,410 208,701 Automotive All 78,985 88,807 127,023 Technology All 118,169 104,479 99,325 Healthcare All 102,221 127,547 124,261 Financials All 112,351 110,069 104,713 Transportation and Travel/Lodging All 88,958 86,419 56,955 Other All 133,980 152,028 138,556 $ 1,415,803 $ 1,476,203 $ 1,513,779 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 twelve 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, 2019 , 2018 and 2017 : Twelve Months Ended December 31, Geographic Location Reportable Segment 2019 2018 2017 United States All $ 1,116,045 $ 1,153,191 $ 1,172,364 Canada All, excluding Media Services 105,067 124,001 123,093 Other All, excluding Media Services and Domestic Creative 194,691 199,011 218,322 $ 1,415,803 $ 1,476,203 $ 1,513,779 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 $66,119 and $64,362 at December 31, 2019 and December 31, 2018 , 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 $30,133 and $42,369 at December 31, 2019 and December 31, 2018 , 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 on the Company’s Consolidated Balance Sheets . Advance billings at December 31, 2019 and December 31, 2018 were $171,742 and $138,505 , respectively. The increase in the advance billings balance of $33,237 for the twelve months ended December 31, 2019 was primarily driven by cash payments received or due in advance of satisfying our performance obligations, offset by $121,659 of revenues recognized that were included in the advance billings balances as of December 31, 2018 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, 2019 and December 31, 2018 were not materially impacted by write offs, impairment losses or any other factors. Practical Expedients As part of the adoption of ASC 606, the Company applied the practical expedient to not disclose information about remaining performance obligations that have original expected durations of one year or less. 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 $49,013 of unsatisfied performance obligations as of December 31, 2019 , of which we expect to recognize approximately 42% in 2020 and 58% in 2021 .

Income (Loss) Per Common Share

Income (Loss) Per Common Share	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Loss Per Common Share	Income (Loss) Per Common Share The following table sets forth the computation of basic and diluted income (loss) per common share: Twelve Months Ended December 31, 2019 2018 2017 Numerator: Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Accretion on convertible preference shares (12,304 ) (8,355 ) (6,352 ) Net income allocated to convertible preference shares — — (29,902 ) Net income (loss) attributable to MDC Partners Inc. common shareholders $ (16,994 ) $ (132,088 ) $ 205,594 Adjustment to net income allocated to convertible preference shares — — 106 Numerator for dilutive income (loss) per common share: Net income (loss) attributable to MDC Partners Inc. common shareholders $ (16,994 ) $ (132,088 ) $ 205,700 Denominator: Basic weighted average number of common shares outstanding 69,132,100 57,218,994 55,255,797 Effect of dilutive securities: Impact of stock options and non-vested stock under employee stock incentive plans — — 225,989 Diluted weighted average number of common shares outstanding 69,132,100 57,218,994 55,481,786 Basic $ (0.25 ) $ (2.31 ) $ 3.72 Diluted $ (0.25 ) $ (2.31 ) $ 3.71 Anti-dilutive stock awards 5,450,426 1,442,518 0 Restricted stock and restricted stock unit awards of 135,386 , 1,012,637 and 1,443,921 as of December 31, 2019 , 2018 and 2017 respectively, which are contingent upon the Company meeting a cumulative three year earnings target and contingent upon continued employment, are excluded from the computation of diluted income per common share as the contingencies were not satisfied at December 31, 2019 , 2018 and 2017 , respectively. In addition, there were 145,000 , 95,000 , and 95,000 Preference Shares outstanding which were convertible into 26,656,285 , 10,970,714 , and 10,135,244 Class A common shares at December 31, 2019 , 2018 , and 2017, respectively. These Preference Shares were anti-dilutive for each period presented in the table above and are therefore excluded from the diluted income (loss) per common share calculation.

Fixed Assets Fixed Assets

Fixed Assets Fixed Assets	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Fixed Assets	Fixed Assets The following is a summary of the Company’s fixed assets as of December 31: 2019 2018 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 93,224 $ (69,687 ) $ 23,537 $ 100,276 $ (73,060 ) $ 27,216 Leasehold improvements 117,409 (59,892 ) 57,517 116,459 (55,486 ) 60,973 $ 210,633 $ (129,579 ) $ 81,054 $ 216,735 $ (128,546 ) $ 88,189 Depreciation expense for the years ended December 31, 2019 , 2018 , and 2017 was $25,133 , $27,111 and $23,873 , respectively.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets As of December 31, goodwill was as follows: Goodwill Global Integrated Agencies Domestic Creative Agencies Specialist Communications Media Services All Other Total Balance at December 31, 2017 $ 359,071 $ 36,980 $ 78,706 $ 160,057 $ 201,121 $ 835,935 Acquired goodwill — — 4,816 — 32,776 37,592 Impairment loss recognized (17,828 ) — — (52,041 ) (4,691 ) (74,560 ) Transfer of goodwill between segments 17,081 2,066 — 3,773 (22,920 ) — Transfer of goodwill to asset held for sale (1) — — — — (45,224 ) (45,224 ) Foreign currency translation (5,169 ) (266 ) (19 ) (443 ) (6,891 ) (12,788 ) Balance at December 31, 2018 $ 353,155 $ 38,780 $ 83,503 $ 111,346 $ 154,171 $ 740,955 Acquired goodwill — — — — 1,025 1,025 Impairment loss recognized — — — — (4,099 ) (4,099 ) Transfer of goodwill between segments (2) (85,766 ) 119,097 (5,006 ) (24,119 ) (4,206 ) — Transfer of goodwill to asset held for sale — — — — — — Foreign currency translation 775 402 176 — 1,440 2,793 Balance at December 31, 2019 $ 268,164 $ 158,279 $ 78,673 $ 87,227 $ 148,331 $ 740,674 (1) See Note 4 of the Notes to the Consolidated Financial Statements included herein for additional information. (2) Transfers of goodwill relate to changes in segments. The Company recognized an impairment of goodwill of $4,099 for the twelve months ended December 31, 2019. The impairment consisted of the write-down of goodwill equal to the excess carrying value above the fair value of one reporting unit within the All Other category. The Company recognized an impairment of goodwill and other assets of $80,057 for the twelve months ended December 31, 2018 . The impairment primarily consisted of the write-down of goodwill equal to the excess carrying value above the fair value of three reporting units, one in each of the Global Integrated Agencies reportable segment, the Media Services reportable segment and within the All Other category. In 2018, the Company also recognized the full write-down of a trademark totaling $3,180 for a reporting unit within the Global Integrated Agencies reportable segment. The trademark is no longer in active use given its merger with another reporting unit. The Company recognized an impairment of goodwill of $4,415 for the twelve months ended December 31, 2017 . The impairment primarily consisted of the write-down of goodwill equal to the excess carrying value above the fair value of two reporting units, one in each of the Global Integrated Agencies reportable segment and the Media Services reportable segment. The total accumulated goodwill impairment charges as of December 31, 2019 and 2018, were $177,304 and $173,205 , respectively. As of December 31, the gross and net amounts of acquired intangible assets other than goodwill were as follows: Years Ended December 31, Intangible Assets 2019 2018 Trademark (indefinite life) $ 14,600 $ 14,600 Customer relationships – gross $ 58,211 $ 76,365 Less accumulated amortization (32,671 ) (42,180 ) Customer relationships – net $ 25,540 $ 34,185 Other intangibles – gross $ 28,695 $ 31,421 Less accumulated amortization (13,942 ) (12,441 ) Other intangibles – net $ 14,753 $ 18,980 Total intangible assets $ 101,506 $ 122,386 Less accumulated amortization (46,613 ) (54,621 ) Total intangible assets – net $ 54,893 $ 67,765 The weighted average amortization period for customer relationships is seven years and other intangible assets 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, 2019, 2018, and 2017 was $11,828 , $17,290 , and $17,125 , respectively. The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2020 $ 9,481 2021 8,098 2022 7,547 2023 7,089 Thereafter 8,078

Deferred Acquisition Considerat

Deferred Acquisition Consideration	12 Months Ended
	Dec. 31, 2019
Business Combinations [Abstract]
Deferred Acquisition Consideration	Acquisitions and Dispositions 2019 Acquisition 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 of the acquisition date, the fair value of the additional interest acquired was $6,005 . The fair value was measured using a discounted cash flow model. 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 of the acquisition date, the fair value of the additional interest acquired was $20,178 . The fair value was measured using a discounted cash flow model. 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 million in the aggregate. The sale resulted in a loss of approximately $3 million , which was included in Other, net within the Condensed Consolidated Statement of Operations. Assets and Liabilities Held for Sale - Change in Plan to Sell In the fourth quarter of 2018, the Company initiated a process to sell its ownership interest in a foreign office within the Global Integrated Agencies reportable segment. The assets and liabilities of the entity were classified as Assets and Liabilities held for sale, at their fair value less cost to sell, within the Consolidated Balance Sheet as of December 31, 2018. In the second quarter of 2019, following the appointment of Mark Penn as CEO, management changed its strategy and plan to sell the foreign office. In the second quarter of 2019, in connection with management’s decision, the amounts classified within assets and liabilities held for sale were reclassified into the respective line items within the Consolidated Balance Sheets . 2018 Acquisitions In 2018, the Company entered into various transactions in connection with certain of its majority-owned entities. These transactions were for an aggregate purchase price of $56,463 , resulting in an increase in contingent deferred consideration liabilities as of the acquisition dates of $16,174 , reduced redeemable noncontrolling interests of $9,790 , a net increase in noncontrolling interests equity of $15,411 , increased additional paid-in capital of $4,975 , and the issuance of 1,011,561 shares of the Company’s Class A subordinate voting stock. Deferred Acquisition Consideration 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 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, 2019 and December 31, 2018 . December 31, 2019 2018 Beginning balance of contingent payments $ 82,598 $ 119,086 Payments (30,719 ) (54,947 ) Redemption value adjustments (1) 15,451 3,512 Additions - acquisitions and step-up transactions 7,145 14,943 Other (2) 196 4 Ending balance of contingent payments $ 74,671 $ 82,598 Fixed payments 549 1,097 $ 75,220 $ 83,695 (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 cost of services sold and office and general expenses on the Consolidated Statements of Operations. (2) Other primarily consists of translation adjustments. The following table presents the impact to the Company’s statement of operations due to the redemption value adjustments for the contingent deferred acquisition consideration for the twelve months ended December 31, 2019 and 2018 : 2019 2018 (Income) loss attributable to fair value adjustments $ 5,403 $ (3,679 ) Stock-based compensation 10,048 7,191 Redemption value adjustments $ 15,451 $ 3,512

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	Leases Effective January 1, 2019, the Company adopted ASC 842. As a result, comparative prior periods have not been adjusted and continue to be reported under ASC 840. See Note 3 of the Notes to the Consolidated Financial Statements included herein for additional information regarding the Company’s adoption of ASC 842. The policies described herein refer to those in effect as of January 1, 2019. 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 2020 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 noncancelable lease payments, payments based upon an index or rate, payments for optional renewal periods where it is reasonably certain the renewal period will be exercised, and payments for early termination options unless it is reasonably certain the lease will not be terminated early. Lease costs are recognized in the 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, and other variable operating expenses. Such amounts are not included in the measurement of the lease liability and are recognized in the period when the facts and circumstances on which the variable lease payments are based upon occur. 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 2020 through 2032. Sublease income is recognized over the lease term on a straight-line basis. Currently, the Company subleases office space in North America, Europe and Australia. As of December 31, 2019 , the Company has entered into five operating leases for which the commencement date has not yet occurred as the space is being prepared for occupancy by the landlord. Accordingly, these leases represent an obligation of the Company that is not on the Consolidated Balance Sheet as of December 31, 2019 . The aggregate future liability related to these leases is approximately $13.9 million . 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, 2019 : Twelve Months Ended December 31, 2019 Lease Cost: Operating lease cost $ 67,044 Variable lease cost 18,879 Sublease rental income (8,965 ) Total lease cost $ 76,958 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 69,735 Right-of-use assets obtained in exchange for operating lease liabilities $ 269,801 Weighted average remaining lease term (in years) - Operating leases 5.3 Weighted average discount rate - Operating leases 8.6 In the twelve months ended December 31, 2019 , the Company recorded an impairment charge of $3.7 million to reduce the carrying value of four of its right-of-use lease assets and related leasehold improvements. These right-of-use assets were within the Global Integrated Agencies and Media Services segments as well as at Corporate. 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 Goodwill and other asset impairment within the Consolidated Statement of Operations. 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 and 2017 was $65,093 and $64,086 , respectively, offset by $3,671 and $2,797 , respectively, in sublease rental income. The following table presents minimum future rental payments under the Company’s leases at December 31, 2019 and their reconciliation to the corresponding lease liabilities: Maturity Analysis 2020 $ 69,563 2021 59,216 2022 48,593 2023 43,878 2024 37,260 2025 and thereafter 102,552 Total 361,062 Less: Present value discount (93,240 ) Lease liability $ 267,822

Debt

Debt	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt As of December 31, 2019 and 2018 , the Company’s indebtedness was comprised as follows: December 31, 2019 December 31, 2018 Revolving credit agreement $ — $ 68,143 6.50% Senior Notes due 2024 900,000 900,000 Debt issuance costs (12,370 ) (14,036 ) $ 887,630 $ 954,107 Interest expense related to long-term debt for the years ended December 31, 2019 , 2018 , and 2017 was $62,210 , $64,420 and $62,001 , respectively. The amortization of deferred finance costs included in interest expense was $3,346 , $3,193 and $3,022 for the years ended December 31, 2019 , 2018 , and 2017 , respectively. 6.50% 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 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 “6.50% Notes”). The 6.50% Notes were sold in a private placement in reliance on exceptions from registration under the Securities Act of 1933. The 6.50% Notes bear interest, payable semiannually in arrears on May 1 and November 1, at a rate of 6.50% per annum. The 6.50% Notes mature on May 1, 2024 , unless earlier redeemed or repurchased. The 6.50% 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 6.50% 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 6.50% 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 6.50% Notes may require MDC to repurchase any 6.50% Notes held by them at a price equal to 101% of the principal amount of the 6.50% 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 6.50% 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 6.50% 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, 2019 . Amendment to Credit Agreement The Company is party to a $250,000 secured revolving credit facility due May 3, 2021. On March 12, 2019 (the “Amendment Effective Date”), the Company, Maxxcom Inc. (a subsidiary of the Company) (“Maxxcom”) and each of their subsidiaries party thereto entered into an 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. Advances under the Credit Agreement bear interest as follows: (a)(i) LIBOR Rate Loans bear interest at the LIBOR Rate and (ii) Base Rate Loans bear interest at the Base Rate, plus (b) an applicable margin. The initial applicable margin for borrowing is 0.75% in the case of Base Rate Loans and 1.50% in the case of LIBOR 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 Amendment provides financial covenant relief by increasing the total leverage ratio applicable on each testing date after the Amendment Effective Date through the period ending December 31, 2020 from 5.5 :1.0 to 6.25 :1.0. The total leverage ratio applicable on each testing date after December 31, 2020 will revert to 5.5 :1.0. In connection with the Amendment, the Company reduced the aggregate maximum amount of revolving commitments provided by the lenders under the Credit Agreement to $250 million from $325 million . 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, 2019. At December 31, 2019 and December 31, 2018 , the Company had issued undrawn outstanding letters of credit of $4,836 and $4,701 , respectively. Future Principal Repayments Future principal repayments on the 6.50% Notes in the aggregate principal amount of $900 million are due in 2024.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2019
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 2019 2018 2017 Service cost $ — $ — $ — Interest cost on benefit obligation 1,640 1,641 1,725 Expected return on plan assets (1,604 ) (1,948 ) (1,830 ) Curtailment and settlements 626 1,039 — Amortization of actuarial (gains) losses 266 258 222 Net periodic benefit cost $ 928 $ 990 $ 117 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 2019 2018 2017 Discount rate 4.42 % 3.83 % 4.32 % Expected return on plan assets 7.00 % 7.00 % 7.40 % 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 2019 2018 2017 Current year actuarial (gain) loss $ 2,917 $ (520 ) $ 1,558 Amortization of actuarial loss (266 ) (258 ) (222 ) Total recognized in other comprehensive (income) loss 2,651 (778 ) 1,336 Total recognized in net periodic benefit cost and other comprehensive loss $ 3,579 $ 212 $ 1,453 The following table summarizes the change in benefit obligations and fair values of plan assets for the years ended December 31: 2019 2018 2017 Change in benefit obligation: Benefit obligation, Beginning balance $ 37,938 $ 43,750 $ 40,722 Interest Cost 1,640 1,641 1,725 Actuarial (gains) losses 6,127 (3,522 ) 3,088 Benefits paid (2,693 ) (3,931 ) (1,785 ) Benefit obligation, Ending balance 43,012 37,938 43,750 Change in plan assets: Fair value of plan assets, Beginning balance 23,181 27,977 24,482 Actual return on plan assets 4,188 (2,093 ) 3,360 Employer contributions 2,530 1,228 1,920 Benefits paid (2,693 ) (3,931 ) (1,785 ) Fair value of plan assets, Ending balance 27,206 23,181 27,977 Unfunded status $ 15,806 $ 14,757 $ 15,773 Amounts recognized in the balance sheet at December 31 consist of the following: Pension Benefits 2019 2018 Non-current liability $ 15,806 $ 14,757 Net amount recognized $ 15,806 $ 14,757 Amounts recognized in Accumulated Other Comprehensive Loss before income taxes consists of the following components for the years ended December 31: Pension Benefits 2019 2018 Accumulated net actuarial losses $ 15,530 $ 12,878 Amount recognized $ 15,530 $ 12,878 In 2020, the Company estimates that it will recognize $340 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 2019 2018 Discount rate 3.39 % 4.42 % Rate of compensation increase N/A N/A The discount rate assumptions at December 31, 2019 and 2018 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, 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 $ — $ — December 31, 2018 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,736 $ 1,736 $ — $ — Mutual funds 21,445 21,445 — — Total $ 23,181 $ 23,181 $ — $ — The pension plans weighted-average asset allocation for the years ended December 31, 2019 and 2018 are as follows: Target Allocation Actual Allocation 2019 2019 2018 Asset Category: Equity securities 65.0 % 66.7 % 67.0 % Debt securities 30.0 % 28.6 % 25.5 % Cash/cash equivalents and Short term investments 5.0 % 4.7 % 7.5 % 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 2019 , the Company contributed $2,530 to the pension plan. The Company estimates that it will make approximately $2,344 in contributions to the pension plan in 2020. 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 2020 $ 1,885 2021 1,885 2022 1,924 2023 2,198 2024 2,323 Thereafter 11,396

Noncontrolling and Redeemable N

Noncontrolling and Redeemable Noncontrolling Interests	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 were as follows: Noncontrolling Balance, December 31, 2017 $ 11,030 Income attributable to noncontrolling interests 11,785 Distributions made (13,419 ) Other (1) (118 ) Balance, December 31, 2018 $ 9,278 Income attributable to noncontrolling interests 16,156 Distributions made (11,392 ) Other (1) (14 ) Balance, December 31, 2019 $ 14,028 (1) Other primarily consists of cumulative translation adjustments. 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, 2019 2018 2017 Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Transfers from the noncontrolling interest: Increase (decrease) in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests 1,911 10,140 2,315 Net transfers from noncontrolling interests $ 1,911 $ 10,140 $ 2,315 Change from net income (loss) attributable to MDC Partners Inc. and transfers to noncontrolling interests $ (2,779 ) $ (113,593 ) $ 244,163 Redeemable Noncontrolling Interests The following table presents changes in redeemable noncontrolling interests as of December 31, 2019 and 2018 : Years Ended December 31, 2019 2018 Beginning Balance $ 51,546 $ 62,886 Redemptions (14,530 ) (11,943 ) Granted — — Changes in redemption value (3,163 ) 1,067 Currency translation adjustments 3 (464 ) Other (1) 3,117 — Ending Balance $ 36,973 $ 51,546 (1) Other primarily consists of the redeemable noncontrolling interest balance related to a foreign entity that was classified as held for sale as of December 31, 2018 and reclassified in 2019. See Note 4 of the Notes to the Consolidated Financial Statements included herein for further information. 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 2019 to 2024. 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 $36,973 as of December 31, 2019 , consists of $18,891 assuming that the subsidiaries perform over the relevant future periods at their discounted cash flows earnings level and such rights are exercised, $15,336 upon termination of such owner’s employment with the applicable subsidiary or death and $2,746 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. These adjustments will not impact the calculation of earnings (loss) per share if the redemption values are less than the estimated fair values. For the twelve months ended December 31, 2019 , 2018 , and 2017, there was a $0 related impact on the Company’s loss per share calculation.

Commitments, Contingencies and

Commitments, Contingencies and Guarantees	12 Months Ended
	Dec. 31, 2019
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, 2019, 2018, and 2017 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, 2019 , the Company had $4,836 of undrawn letters of credit.

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2019
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, 2019 , the Series 6 Preference Shares accreted at a monthly rate of $6.96 , for total accretion of $3,261 , bringing the aggregate liquidation preference to $53,261 as of December 31, 2019 . The accretion is considered in the calculation of net loss attributable to MDC Partners Inc. common shareholders. See Note 6 of the Notes to the Consolidated Financial Statements included herein for further information regarding the Series 6 Preference Shares. Holders of the Series 6 Preference Shares are entitled to dividends in an amount equal to any dividends that would otherwise have been payable on the Class A Shares issued upon conversion of the Series 6 Preference Shares. The Series 6 Preference Shares are convertible at the Company’s option (i) on and after the two -year anniversary of the Series 6 Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least 125% of the Conversion Price or (ii) after the fifth anniversary of the Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least equal to the Conversion Price. Following certain change in control transactions of the Company in which holders of Series 6 Preference Shares are not entitled to receive cash or qualifying listed securities with a value at least equal to the liquidation preference plus accrued and unpaid dividends, (i) holders will be entitled to cash dividends on the liquidation preference at an increasing rate (beginning at 7% ), and (ii) the Company will have a right to redeem the Series 6 Preference Shares for cash at the greater of their liquidation preference plus accrued and unpaid dividends or their as-converted value. Effective March 18, 2019, the Company’s Board appointed Mark Penn as the Chief Executive Officer (“CEO”) and as a director of the Board. Mr. Penn is manager of Stagwell. Effective April 18, 2019, Mr. Penn was also appointed as Chairman of the Board. Series 4 Convertible Preference Shares On March 7, 2017 (the “Series 4 Issue Date”), the Company issued 95,000 newly created Preference Shares (“Series 4 Preference Shares”) to affiliates of The Goldman Sachs Group, Inc. (collectively, the “Purchaser”) pursuant to a $95,000 private placement. The Company received proceeds of approximately $90,123 , net of fees and estimated expenses, which were primarily used to pay down existing debt under the Company’s credit facility and for general corporate purposes. In connection with the closing of the transaction, the Company increased the size of its Board and appointed one nominee designated by the Purchaser. Except as required by law, the Series 4 Preference Shares do not have voting rights and are not redeemable at the option of the Purchaser. Subsequent to the ninetieth day following the Series 4 Issue Date, the holders of the Series 4 Preference Shares have the right to convert their Series 4 Preference Shares in whole at any time and from time to time and in part at any time and from time to time into a number of Class A Shares equal to the then-applicable liquidation preference divided by the applicable conversion price at such time (the “Conversion Price”). The initial liquidation preference per share of each Series 4 Preference Share is $1,000 . The Conversion Price of a Series 4 Preference Share is subject to customary adjustments for share splits and combinations, dividends, recapitalizations and other matters, including weighted average anti-dilution protection for certain issuances of equity or equity-linked securities. In connection with the anti-dilution protection provision triggered by the issuance of equity securities to Stagwell Holdings, the Conversion Price per Series 4 Preference Share was reduced to $7.42 from the initial Conversion Price of $10.00 . The Series 4 Preference Shares’ liquidation preference accretes at 8.0% per annum, compounded quarterly until the five-year anniversary of the Series 4 Issue Date. During the twelve months ended December 31, 2019 and 2018 , the Series 4 Preference Shares accreted at a monthly rate of approximately $8.17 and $7.55 per Series 4 Preference Share, for total accretion of $9,043 and $8,355 , respectively, bringing the aggregate liquidation preference to $118,751 as of December 31, 2019 . The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. See Note 6 of the Notes to the Consolidated Financial Statements included herein for further information regarding the Series 4 Preference Shares. Holders of the Series 4 Preference Shares are entitled to dividends in an amount equal to any dividends that would otherwise have been payable on the Class A Shares issued upon conversion of the Series 4 Preference Shares. The Series 4 Preference Shares are convertible at the Company’s option (i) on and after the two-year anniversary of the Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least 125% of the Conversion Price or (ii) after the fifth anniversary of the Series 4 Issue Date, if the closing trading price of the Class A Shares over a specified period prior to conversion is at least equal to the Conversion Price. Following certain change in control transactions of the Company in which holders of Series 4 Preference Shares are not entitled to receive cash or qualifying listed securities with a value at least equal to the liquidation preference plus accrued and unpaid dividends, (i) holders will be entitled to cash dividends on the liquidation preference at an increasing rate (beginning at 7% ), and (ii) the Company will have a right to redeem the Series 4 Preference Shares for cash at the greater of their liquidation preference plus accrued and unpaid dividends or their as-converted value. Class A Common Shares (“Class A Shares”) These are an unlimited number of subordinate voting shares, carrying one vote each, with a par value of $0, entitled to dividends equal to or greater than Class B Shares, convertible at the option of the holder into one Class B Share for each Class A Share after the occurrence of certain events related to an offer to purchase all Class B shares. There were 72,150,854 (including the Class A Shares issued to Stagwell) and 57,517,568 Class A Shares issued and outstanding as of December 31, 2019 and 2018 , 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 3,749 and 3,755 Class B Shares issued and outstanding as of December 31, 2019 and 2018 , respectively. Employee Stock Incentive Plan As of December 31, 2019 , a total of 15,650,000 shares have been authorized under our employee stock incentive plan. 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, 2018 452,912 $ 9.15 626,940 $ 9.83 Granted 2,738,141 3.08 490,000 2.54 Vested (276,952 ) 3.03 (294,980 ) 12.46 Forfeited (470,300 ) 8.79 (253,000 ) 3.38 Balance at December 31, 2019 2,443,801 $ 3.11 568,960 $ 5.53 Performance based and time-based awards granted in the twelve months ended December 31, 2018 had a weighted average grant date fair value of $9.17 and $7.38 , respectively. Time-based awards granted in the twelve months ended December 31, 2017 had a weighted average grant date fair value of $8.98 . No performance based awards were granted in 2017 . 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, 2019 , 2018 and 2017 was $4,517 , $3,583 and $7,316 , respectively. At December 31, 2019 , the weighted average remaining contractual life for time based and performance based awards was 1.93 and 2.10 years, respectively. At December 31, 2019 , the unrecognized compensation expense for performance based awards was $5,341 to be recognized over a weighted average period of 2.10 years. At December 31, 2019 , the unrecognized compensation expense for time based awards was $919 to be recognized over a weighted average period of 1.93 years. The following table summarizes information about share option awards: Share Option Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2018 111,866 $ 2.23 $ 4.85 Granted — — — Vested — — — Forfeited — — — Exercised — — — Balance at December 31, 2019 111,866 $ 2.23 $ 4.85 We use the Black-Scholes option-pricing model to estimate the fair value of options granted. No options were granted in 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 three years . The term of these awards is 5 years. The vesting period of these awards is generally commensurate with the requisite service period. At December 31, 2019 , the weighted average remaining contractual life for these awards was 2 years. No options were granted in 2017. No options were exercised during 2019 and 2018. The intrinsic value of options exercised during 2017 was $125 . The aggregate intrinsic value of options outstanding as of December 31, 2019 is nil . As of December 31, 2019 , no options were exercisable. No options vested in 2018 and 2017. At December 31, 2019 , the unrecognized compensation expense for these awards was $150 to be recognized over a weighted average period of 2 years. The cash received from the stock options exercised in 2017 was nil . The following table summarizes information about stock appreciation rights (“SAR”) awards: SAR Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2018 250,800 $ 2.35 $ 6.60 Granted 2,425,000 1.04 3.07 Vested — — — Forfeited (350,000 ) 1.31 5.57 Exercised — — — Balance at December 31, 2019 2,325,800 $ 1.14 $ 3.07 We use the Black-Scholes option-pricing model to estimate the fair value of the SAR awards. SAR awards granted in 2019 vest in equal installments on each of the first three 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. SAR awards granted in 2017 vest on the third anniversary of the grant date and have a grant date fair value of $2.35 . The assumptions for the model were as follows: expected life of 4 years, risk free interest rate of 1.7% , expected volatility of 46.2% 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. As of December 31, 2019 , no SAR awards were exercisable. As of December 31, 2019 , there were no SAR awards that were vested. The aggregate intrinsic value of the SAR awards outstanding as of December 31, 2019 is $885 . No SAR awards were exercised during 2019 and 2018. No SAR awards vested in 2018 and 2017. At December 31, 2019 , the weighted average remaining contractual life for the SAR awards was 1.22 years. At December 31, 2019 , the unrecognized compensation expense for these awards was $1,298 to be recognized over a weighted average period of 1.22 years. For the years ended December 31, 2019 , 2018 and 2017 , $2,460 , $5,892 , and $5,335 was recognized in stock compensation related to all stock compensation awards, respectively. The related income tax benefit for the years ended December 31, 2019 , 2018 and 2017 was $643 , $472 , and $1,401 , respectively.

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2019
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, 2017 $ (13,656 ) $ 11,702 $ (1,954 ) Other comprehensive income before reclassifications — 6,119 6,119 Amounts reclassified from accumulated other comprehensive income (net of tax expense of $223) 555 — 555 Other comprehensive income 555 6,119 6,674 Balance December 31, 2018 $ (13,101 ) $ 17,821 $ 4,720 Other comprehensive loss 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 loss (1,911 ) (7,078 ) (8,989 ) Balance December 31, 2019 $ (15,012 ) $ 10,743 $ (4,269 )

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes On December 22, 2017, the U.S. government enacted the Tax Act. The Tax Act makes broad and complex changes to the U.S. tax code including but not limited to a reduction in the U.S. federal corporate tax rate from 35.0% to 21.0% , effective for tax years beginning after December 31, 2017 and a one-time transition tax on the mandatory deemed repatriation of cumulative foreign earnings. 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: 2019 2018 2017 Income (Loss): U.S. $ (16,711 ) $ (68,698 ) $ 48,053 Non-U.S. 38,358 (11,709 ) 39,025 $ 21,647 $ (80,407 ) $ 87,078 The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2019 2018 2017 Current tax provision U.S. federal $ 2,638 $ 444 $ (1,657 ) U.S. state and local 12 2 98 Non-U.S. 2,875 7,584 6,514 5,525 8,030 4,955 Deferred tax provision (benefit): U.S. federal 4,799 (9,315 ) (172,873 ) U.S. state and local 1,183 (2,990 ) (7,775 ) Non-U.S. (974 ) 35,878 7,629 5,008 23,573 (173,019 ) Income tax expense (benefit) $ 10,533 $ 31,603 $ (168,064 ) 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: 2019 2018 2017 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ 21,647 $ (80,407 ) $ 87,078 Statutory income tax rate 21.0 % 21.0 % 35.0 % Tax expense (benefit) using U.S. statutory income tax rate 4,546 (16,886 ) 30,477 State and foreign taxes 1,194 (2,988 ) 8,863 Non-deductible stock-based compensation 3,823 1,512 1,441 Other non-deductible expense 709 10,091 (220 ) Change to valuation allowance (2,830 ) 49,482 (103,212 ) Effect of the difference in U.S. federal and local statutory rates 1,422 (152 ) (2,939 ) Impact of tax reform — — (100,472 ) Noncontrolling interests (3,566 ) (2,674 ) (4,413 ) Impact of foreign operations 3,646 1,711 (2,453 ) Adjustment to deferred tax balances — (8,865 ) — Other, net 1,589 372 4,864 Income tax expense (benefit) $10,533 $31,603 $(168,064) Effective income tax rate 48.7% (39.3)% (193.0)% The Company has evaluated the usefulness of our rate reconciliation presented in prior periods which utilized the Canadian statutory tax rate of 26.5%. As the majority of our business operations and shareholders are located in the U.S., we believe using the U.S. statutory rate is more informative. The period 2017 in the table above has been conformed to reflect the U.S. statutory rate. Income tax expense for the twelve months ended December 31, 2019 was $ 10,533 (associated with a pretax income of $21,647 ) compared to an income tax expense of $31,603 (associated with pretax loss of $80,407 ) for the twelve months ended December 31, 2018 . Income tax expense in 2019 included the impact of reducing a valuation allowance primarily associated with Canadian deferred tax assets. Income tax expense in 2018 included the impact of increasing a valuation allowance primarily associated with Canadian deferred tax assets. Income taxes receivable were $5,025 and $4,388 at December 31, 2019 and 2018 , respectively, and were included in other current assets on the balance sheet. Income taxes payable were $11,722 and $10,045 at December 31, 2019 and 2018 , 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: 2019 2018 Deferred tax assets: Capital assets and other $ — $ 905 Net operating loss carry forwards 73,852 70,646 Interest deductions 16,797 8,911 Refinancing charge 669 2,926 Goodwill and intangibles 114,922 123,504 Stock compensation 1,736 2,101 Pension plan 4,414 3,872 Unrealized foreign exchange 11,373 14,645 Capital loss carry forwards 13,081 11,827 Right-of-use assets and accounting reserves 77,824 8,280 Gross deferred tax asset 314,668 247,617 Less: valuation allowance (65,649 ) (68,479 ) Net deferred tax assets 249,019 179,138 Deferred tax liabilities: Lease liabilities $ (67,613 ) $ — Withholding taxes (546 ) — Capital assets (382 ) — Goodwill amortization (98,677 ) (91,726 ) Total deferred tax liabilities (167,218 ) (91,726 ) Net deferred tax asset (liability) $ 81,801 $ 87,412 Disclosed as: Deferred tax assets $ 85,988 $ 92,741 Deferred tax liabilities (4,187 ) (5,329 ) $ 81,801 $ 87,412 The Company has U.S. federal net operating loss carry forwards of $45,094 and non-U.S. net operating loss carry forwards of $146,037 , which expire in years 2020 through 2039. The Company also has total indefinite loss carry forwards of $205,050 . These indefinite loss carry forwards consist of $106,329 relating to the U.S. and $98,721 related to capital losses from the Canadian operations. In addition, the Company has net operating loss carry forwards for various state taxing jurisdictions of approximately $176,174 . 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, future taxable income, and tax planning strategies. A change to these factors could impact the estimated valuation allowance and income tax expense. As of December 31, 2018 , the Company maintained a valuation allowance against foreign net deferred tax assets of $68,479 as it believed it was more likely than not that some or all of the deferred tax assets would not be realized. This assessment was based on the Company’s historical losses and uncertainties as to the amount of future taxable income. As of December 31, 2019 , the Company evaluated positive and negative evidence in determining the likelihood that it will be able to realize all or some portion of its deferred tax assets prior to their expiration. As of December 31, 2019 , the Company’s Canadian three-year cumulative pre-tax income increased compared to the period ended December 31, 2018 and the Company decreased its overall valuation allowance by $2,830 . The related effect on the accompanying consolidated statements of operations and comprehensive income or loss resulted in the Company recording a U.S. income tax benefit of $2,830 for the year ended December 31, 2019. The Company has historically asserted that its unremitted foreign earnings are permanently reinvested, and therefore has not recorded income taxes on such amounts. The Company reevaluated its global cash needs and as a result determined that approximately $5,462 of undistributed foreign earnings from certain international entities are no longer subject to the permanent reinvestment assertion. We recorded a tax expense of $546 representing our estimate of the tax costs associated with this change to our assertion. 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. As of December 31, 2019 and 2018 , the Company recorded a liability for unrecognized tax benefits as well as applicable penalties and interest in the amount of $1,107 and $973 , respectively. As of December 31, 2019 and 2018 , accrued penalties and interest included in unrecognized tax benefits were approximately $111 and $87 , respectively. The Company identified an uncertainty relating to the future tax deductibility of certain intercompany fees. To the extent that such future benefit will be established, the resolution of this position will have no effect with respect to the consolidated financial statements. If these unrecognized tax benefits were to be recognized, it would affect the Company’s effective tax rate. 2019 2018 2017 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 887 $ 1,433 $ 1,465 Current year positions 275 — 489 Prior period positions — 7 (436 ) Settlements — (314 ) — Lapse of statute of limitations (166 ) (239 ) (85 ) Unrecognized tax benefits - Ending Balance $ 996 $ 887 $ 1,433 It is reasonably possible that the amount of unrecognized tax benefits could decrease by a range of $200 to $300 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 U.S. Internal Revenue Service (“IRS”) concluded its review of the 2016 tax year and all years prior to 2016 are closed. The statute of limitations has also expired in non-U.S. jurisdictions through 2014.

Financial Instruments (Notes)

Financial Instruments (Notes)	12 Months Ended
	Dec. 31, 2019
Investments, All Other Investments [Abstract]
Financial Instruments	Financial Instruments Financial assets, which include cash and cash equivalents and accounts receivable, have carrying values which approximate fair value due to the short-term nature of these assets. Financial liabilities with carrying values approximating fair value due to short-term maturities include accounts payable. Deferred acquisition consideration is recorded at fair value. The revolving credit agreement is a variable rate debt, the carrying value of which approximates fair value. The Company’s notes are a fixed rate debt instrument recorded at carrying value. See Note 19 of the Notes to the Consolidated Financial Statements included herein for additional information on the fair value. The fair value of financial commitments and letters of credit are based on the stated value of the underlying instruments, if any.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 : December 31, 2019 December 31, 2018 Carrying Fair Value Carrying Fair Value Liabilities: 6.50% Senior Notes due 2024 $ 900,000 $ 812,250 $ 900,000 $ 834,750 Our long-term debt includes fixed rate debt. The fair value of this instrument is based on quoted market prices in markets that are not active. Therefore, this debt is classified as Level 2 within the fair value hierarchy. Financial Liabilities Measured at Fair Value on a Recurring Basis Contingent deferred acquisition consideration 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 that may be dependent upon future events, such as the growth rate of the earnings of the relevant subsidiary during the contractual period and, in some cases, the currency exchange rate as of the date of payment (Level 3). See Note 9 of the Notes to the Consolidated Financial Statements included herein for additional information regarding contingent deferred acquisition consideration. At December 31, 2019 and 2018 , the carrying amount of the Company’s financial instruments, including cash and cash equivalents, accounts receivable and accounts payable, approximated fair value because of their short-term maturity. Non-financial Assets and Liabilities that are Measured at Fair Value on a Nonrecurring Basis Certain non-financial assets are measured at fair value on a nonrecurring basis, primarily goodwill, intangible assets (a Level 3 fair value assessment) and right-of-use lease assets (a 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 $4.1 million for the twelve months ended December 31, 2019 as compared to an impairment of goodwill, intangible assets, and other assets of $80.1 million for the twelve months ended December 31, 2018 . See Note 2 and 8 of the Notes to the Consolidated Financial Statements for information related to the measurement of the fair value of goodwill. In addition, the Company recognized an impairment charge of $3.7 million to reduce the carrying value of certain right-of-use lease assets and related leasehold improvements in the twelve months ended December 31, 2019 . See Note 10 of the Notes to the Consolidated Financial Statements included herein for further information.

Related Party Transactions (Not

Related Party Transactions (Notes)	12 Months Ended
	Dec. 31, 2019
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 an affiliate of Stagwell, in which the affiliate and the Partner Firm will collaborate to provide various services to a client of the Partner Firm. Under the arrangement the Partner Firm will pay the affiliate, for services provided by the affiliate, approximately $655 which is expected to be recognized through the end of 2020. As of December 31, 2019, $393 was owed to the affiliate. On February 14, 2020, Sloane sold substantially all its assets and certain liabilities to an affiliate of Stagwell. See Note 1 of the Notes to the Consolidated Financial Statements for information related to this transaction. The Company entered into an agreement commencing on January 1, 2020 to sublease office space through July 2021 to a company whose chairman is a member of the Company’s Board of Directors. The total future rental income related to the sublease is approximately $350 .

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2019
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”) 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 results of operations for each operating segment, together with a qualitative assessment to determine if operating segments have similar operating characteristics. Due to changes in the composition of certain businesses and the Company’s internal management and reporting structure during 2019, reportable segment results for the 2018 and 2017 periods presented have been recast to reflect the reclassification of certain businesses between segments. The changes were as follows: • Doner, previously within the Global Integrated Agencies reportable segment is now included within the Domestic Creative Agencies reportable segment. • HL Group Partners, previously within the Specialist Communications reportable segment, and Redscout, previously within the All Other category, are now included in the Yes & Company operating segment. The Yes & Company operating segment previously within the Media Services reportable segment is now included within the Domestic Creative Agencies reportable segment. • Attention, previously within the Forsman & Bodenfors operating segment, has operationally merged into MDC Media Partners, which is included within the Media Services reportable segment. • Varick Media, previously within the Yes & Company operating segment, is now included within MDC Media Partners, which is included within the Media Services reportable segment. The four reportable segments that result from applying the aggregation criteria are as follows: “Global Integrated Agencies”; “Domestic Creative Agencies”; “Specialist Communications”; and “Media Services.” In addition, the Company combines and discloses those operating segments that do not meet the aggregation criteria as “All Other.” The Company also reports corporate expenses, as further detailed below, as “Corporate.” • The Global Integrated Agencies reportable segment is comprised of the Company’s four global, integrated operating segments (72andSunny, Anomaly, Crispin Porter + Bogusky, and Forsman & Bodenfors) serving multinational clients around the world. These operating segments share similar characteristics related to (i) the nature of their services; (ii) the type of global 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. The Company believes the historic and expected average long-term profitability is similar among the operating segments aggregated in the Global Integrated Agencies reportable segment. The operating segments within the Global Integrated Agencies reportable segment provides a range of different services for its clients, including strategy, creative and production for advertising campaigns across a variety of platforms (print, digital, social media, television broadcast). • The Domestic Creative Agencies reportable segment is comprised of seven operating segments that are primarily national advertising agencies (Colle McVoy, Doner, Laird + Partners, Mono Advertising, Union, Yamamoto, and Yes & Company) leveraging creative capabilities at their core. These operating segments share similar characteristics related to (i) the nature of their services; (ii) the type of domestic client accounts and the methods used to provide services; and (iii) the extent to which they may be impacted by domestic economic and policy factors within North America. In addition, these operating segments compete with each other for new business and from time to time have business move between them. The Company believes the historic and expected average long-term results of operations is similar among the operating segments aggregated in the Domestic Creative Agencies reportable segment. The operating segments within the Domestic Creative Agencies reportable segment provide similar services as the Global Integrated Agencies. • The Specialist Communications reportable segment is comprised of four operating segments that are each communications agencies (Allison & Partners, Hunter, KWT Global, and Veritas) with core service offerings in public relations and related communications services. These operating segments share similar characteristics related to (i) the nature of their services; (ii) the type of client accounts and the methods used to provide services; (iii) the extent to which they may be impacted by domestic economic and policy factors within North America; and (iv) the regulatory environment regarding public relations and social media. In addition, these operating segments compete with each other for new business and from time to time have business move between them. The Company believes the historic and expected average long-term results of operations is similar among the operating segments aggregated in the Specialist Communications reportable segment. The operating segments within the Specialist Communications reportable segment provide public relations and communications services including strategy, editorial, crisis support or issues management, media training, influencer engagement, and events management. • The Media Services reportable segment is comprised of a single operating segment known as MDC Media Partners. MDC Media Partners, which operates primarily in North America, performs media buying and planning as its core competency across a range of platforms (out-of-home, paid search, social media, lead generation, programmatic, television broadcast). • All Other consists of the Company’s remaining operating segments that provide a range of diverse 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 6Degrees Communications, Concentric Partners, Gale Partners, Kenna, Kingsdale (through the date of sale on March 8, 2019), Instrument, Relevent, Team, Vitro, and Y Media Labs. The nature of the specialist services provided by these operating segments vary among each other and from those operating segments aggregated into the reportable segments. This results in these operating segments having current and long-term performance expectations inconsistent with those operating segments aggregated in the reportable segments. The operating segments within All Other provide a range of diverse marketing communication services, including application and website design and development, data and analytics, experiential marketing, customer research management, creative services, and branding. • 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. See Note 1 of the Notes to the Consolidated Financial statements for information regarding our assessment of changes to our reportable segments in our fiscal year 2020. Years Ended December 31, 2019 2018 2017 Revenue: Global Integrated Agencies $ 598,184 $ 610,290 $ 688,011 Domestic Creative Agencies 230,718 246,642 277,587 Specialist Communications 180,591 163,367 153,506 Media Services 97,825 121,859 150,198 All Other 308,485 334,045 244,477 Total $ 1,415,803 $ 1,476,203 $ 1,513,779 Segment operating income (loss): Global Integrated Agencies $ 58,933 $ 63,972 $ 60,891 Domestic Creative Agencies 28,254 51 38,221 Specialist Communications 23,822 17,316 19,978 Media Services (5,398 ) (51,169 ) 13,900 All Other 20,397 34,683 39,825 Corporate (45,768 ) (55,157 ) (40,856 ) Total $ 80,240 $ 9,696 $ 131,959 Other Income (expense): Interest expense and finance charges, net $ (64,942 ) $ (67,075 ) $ (64,364 ) Foreign exchange gain (loss) 8,750 (23,258 ) 18,137 Other, net (2,401 ) 230 1,346 Income (loss) before income taxes and equity in earnings of non-consolidated affiliates 21,647 (80,407 ) 87,078 Income tax expense (benefit) 10,533 31,603 (168,064 ) Income (loss) before equity in earnings of non-consolidated affiliates 11,114 (112,010 ) 255,142 Equity in earnings of non-consolidated affiliates 352 62 2,081 Net income (loss) 11,466 (111,948 ) 257,223 Net income attributable to the noncontrolling interest (16,156 ) (11,785 ) (15,375 ) Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Years Ended December 31, 2019 2018 2017 Depreciation and amortization: Global Integrated Agencies $ 16,572 $ 21,179 $ 21,206 Domestic Creative Agencies 4,843 5,052 5,143 Specialist Communications 2,577 4,113 4,567 Media Services 3,261 2,693 3,709 All Other 10,208 12,397 7,751 Corporate 868 762 1,098 Total $ 38,329 $ 46,196 $ 43,474 Stock-based compensation: Global Integrated Agencies $ 26,207 $ 8,095 $ 14,666 Domestic Creative Agencies 1,532 2,623 2,301 Specialist Communications 209 372 2,160 Media Services 20 276 614 All Other 1,192 2,391 2,475 Corporate 1,880 4,659 2,134 Total $ 31,040 $ 18,416 $ 24,350 Capital expenditures: Global Integrated Agencies $ 8,223 $ 8,731 $ 18,897 Domestic Creative Agencies 3,044 2,692 4,695 Specialist Communications 1,166 3,553 1,181 Media Services 194 806 3,035 All Other 5,933 4,415 5,127 Corporate 36 67 23 Total $ 18,596 $ 20,264 $ 32,958 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 2019 $ 68,497 $ 4,475 $ 8,082 $ 81,054 2018 $ 76,781 $ 4,779 $ 6,629 $ 88,189 Goodwill and Intangible Assets 2019 $ 668,567 $ 64,842 $ 62,158 $ 795,567 2018 $ 679,344 $ 61,748 $ 67,628 $ 808,720 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. 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: 2019 $ 1,116,045 $ 105,067 $ 194,691 $ 1,415,803 2018 $ 1,153,191 $ 124,001 $ 199,011 $ 1,476,203 2017 $ 1,172,364 $ 123,093 $ 218,322 $ 1,513,779

Quarterly Results of Operations

Quarterly Results of Operations	12 Months Ended
	Dec. 31, 2019
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: 2019 $ 328,791 $ 362,130 $ 342,907 $ 381,975 2018 $ 326,968 $ 379,743 $ 375,830 $ 393,662 Cost of services sold: 2019 $ 237,154 $ 240,749 $ 222,448 $ 260,725 2018 $ 243,030 $ 253,390 $ 238,690 $ 256,088 Net Income (loss): 2019 $ 316 $ 7,333 $ 5,513 $ (1,696 ) 2018 $ (28,519 ) $ 5,951 $ (13,667 ) $ (75,713 ) Net income (loss) attributable to MDC Partners Inc.: 2019 $ (113 ) $ 4,290 $ (1,752 ) $ (7,115 ) 2018 $ (29,416 ) $ 3,406 $ (16,125 ) $ (81,598 ) Income (loss) per common share: Basic 2019 $ (0.04 ) $ 0.01 $ (0.07 ) $ (0.15 ) 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) Diluted 2019 $ (0.04 ) $ 0.01 $ (0.07 ) $ (0.15 ) 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) 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) have been affected as follows: • The fourth quarter of 2019 and 2018 included a foreign exchange gain of $4,349 and a loss of $13,324 , respectively. • The fourth quarter of 2019 and 2018 included stock-based compensation charges of $18,408 and $1,534 , respectively. • The fourth quarter of 2019 and 2018 included changes in deferred acquisition resulting in income of $9,030 and $8,979 , respectively. • The fourth quarter of 2019 and 2018 included goodwill, right-of-use assets and related leasehold improvement impairment charges of $5,875 and goodwill and other asset impairment charges of $56,732 , respectively. • The fourth quarter of 2019 included income tax benefit of $ 2,830 relating to the decrease to the Company’s valuation allowance. The fourth quarter of 2018 included income tax expense related to the increase of the Company’s valuation allowance of $49,447 .

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
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 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 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 and other identifiable intangible assets. The measurement of fair value requires the use of techniques based on observable and unobservable inputs. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect market assumptions. When available, the Company uses quoted market prices in active markets to determine the fair value of its financial instruments and classifies such items in Level 1. In some cases, quoted market prices are used for similar instruments in active markets and the Company classifies such items in Level 2.
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, 2019 or December 31, 2018 . 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, 2019, 2018, or 2017. 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 ASC 842, Leases. As a result, comparative prior periods have not been adjusted and continue 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 3 and 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, are included in Investments in non-consolidated affiliates within the Consolidated Balance Sheets. 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 (cost method 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, 2019 and 2018 was $9,854 and $8,072 , 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 unless 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 and Indefinite Lived Intangibles	Goodwill and Indefinite Lived Intangibles . Goodwill (the excess of the acquisition cost over the fair value of the net assets acquired) and an indefinite life intangible asset (a trademark) acquired as a result of a business combination which are not subject to amortization are tested for impairment annually as of October 1st of each year, or more frequently if indicators of potential impairment exist. For goodwill, impairment is assessed at the reporting unit level. 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 2019 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. Indefinite-lived intangible assets are primarily evaluated on an annual basis, generally in conjunction with the Company’s evaluation of goodwill balances.
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. 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. The Company’s acquisition model typically provides for an initial payment at closing and for future additional contingent purchase price obligations. 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. Changes in such estimated values are recorded in the results of operations. 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 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 . Consistent with past practice of acquiring a majority ownership position, 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. 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 results of operations.
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 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. 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, 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. 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.
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 $11,909 , $11,136 and $10,031 for the years ended December 31, 2019 , 2018 , and 2017 , 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 (loss) income. 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	Adopted In The Current Reporting Period Effective January 1, 2019, the Company adopted ASC 842. As a result, comparative prior periods have not been adjusted and continue to be reported under ASC 840, Leases. With the adoption of ASC 842, the Company has elected to apply the package of practical expedients: (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized costs continue to qualify as initial indirect costs. Additionally, the Company elected the practical expedient to not separate non-lease components from lease components for all operating leases. The adoption of ASC 842 had a material impact on the Company’s Consolidated Balance Sheets , resulting in the recognition, on January 1, 2019, of a lease liability of $299,243 which represents the present value of the remaining lease payments, and a right-of-use lease asset of $254,245 which represents the lease liability, offset by adjustments as appropriate under ASC 842. The adoption of ASC 842 did not have a material impact on the Company’s other Consolidated Financial Statements .

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 , 2018 and 2017 : Twelve Months Ended December 31, Geographic Location Reportable Segment 2019 2018 2017 United States All $ 1,116,045 $ 1,153,191 $ 1,172,364 Canada All, excluding Media Services 105,067 124,001 123,093 Other All, excluding Media Services and Domestic Creative 194,691 199,011 218,322 $ 1,415,803 $ 1,476,203 $ 1,513,779
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, 2019 , 2018 and 2017 : Twelve Months Ended December 31, Industry Reportable Segment 2019 2018 2017 Food & Beverage All $ 280,094 $ 313,368 $ 313,786 Retail All 148,851 152,552 178,152 Consumer Products All 167,324 162,524 162,307 Communications All 184,870 178,410 208,701 Automotive All 78,985 88,807 127,023 Technology All 118,169 104,479 99,325 Healthcare All 102,221 127,547 124,261 Financials All 112,351 110,069 104,713 Transportation and Travel/Lodging All 88,958 86,419 56,955 Other All 133,980 152,028 138,556 $ 1,415,803 $ 1,476,203 $ 1,513,779

Income (Loss) Per Common Share

Income (Loss) Per Common Share (Tables)	12 Months Ended
	Dec. 31, 2019
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share	The following table sets forth the computation of basic and diluted income (loss) per common share: Twelve Months Ended December 31, 2019 2018 2017 Numerator: Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Accretion on convertible preference shares (12,304 ) (8,355 ) (6,352 ) Net income allocated to convertible preference shares — — (29,902 ) Net income (loss) attributable to MDC Partners Inc. common shareholders $ (16,994 ) $ (132,088 ) $ 205,594 Adjustment to net income allocated to convertible preference shares — — 106 Numerator for dilutive income (loss) per common share: Net income (loss) attributable to MDC Partners Inc. common shareholders $ (16,994 ) $ (132,088 ) $ 205,700 Denominator: Basic weighted average number of common shares outstanding 69,132,100 57,218,994 55,255,797 Effect of dilutive securities: Impact of stock options and non-vested stock under employee stock incentive plans — — 225,989 Diluted weighted average number of common shares outstanding 69,132,100 57,218,994 55,481,786 Basic $ (0.25 ) $ (2.31 ) $ 3.72 Diluted $ (0.25 ) $ (2.31 ) $ 3.71

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following is a summary of the Company’s fixed assets as of December 31: 2019 2018 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 93,224 $ (69,687 ) $ 23,537 $ 100,276 $ (73,060 ) $ 27,216 Leasehold improvements 117,409 (59,892 ) 57,517 116,459 (55,486 ) 60,973 $ 210,633 $ (129,579 ) $ 81,054 $ 216,735 $ (128,546 ) $ 88,189

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	As of December 31, goodwill was as follows: Goodwill Global Integrated Agencies Domestic Creative Agencies Specialist Communications Media Services All Other Total Balance at December 31, 2017 $ 359,071 $ 36,980 $ 78,706 $ 160,057 $ 201,121 $ 835,935 Acquired goodwill — — 4,816 — 32,776 37,592 Impairment loss recognized (17,828 ) — — (52,041 ) (4,691 ) (74,560 ) Transfer of goodwill between segments 17,081 2,066 — 3,773 (22,920 ) — Transfer of goodwill to asset held for sale (1) — — — — (45,224 ) (45,224 ) Foreign currency translation (5,169 ) (266 ) (19 ) (443 ) (6,891 ) (12,788 ) Balance at December 31, 2018 $ 353,155 $ 38,780 $ 83,503 $ 111,346 $ 154,171 $ 740,955 Acquired goodwill — — — — 1,025 1,025 Impairment loss recognized — — — — (4,099 ) (4,099 ) Transfer of goodwill between segments (2) (85,766 ) 119,097 (5,006 ) (24,119 ) (4,206 ) — Transfer of goodwill to asset held for sale — — — — — — Foreign currency translation 775 402 176 — 1,440 2,793 Balance at December 31, 2019 $ 268,164 $ 158,279 $ 78,673 $ 87,227 $ 148,331 $ 740,674 (1) See Note 4 of the Notes to the Consolidated Financial Statements included herein for additional information. (2) Transfers of goodwill relate to changes in segments.
Schedule of Intangible Assets and Goodwill	As of December 31, the gross and net amounts of acquired intangible assets other than goodwill were as follows: Years Ended December 31, Intangible Assets 2019 2018 Trademark (indefinite life) $ 14,600 $ 14,600 Customer relationships – gross $ 58,211 $ 76,365 Less accumulated amortization (32,671 ) (42,180 ) Customer relationships – net $ 25,540 $ 34,185 Other intangibles – gross $ 28,695 $ 31,421 Less accumulated amortization (13,942 ) (12,441 ) Other intangibles – net $ 14,753 $ 18,980 Total intangible assets $ 101,506 $ 122,386 Less accumulated amortization (46,613 ) (54,621 ) Total intangible assets – net $ 54,893 $ 67,765
Finite-lived Intangible Assets Amortization Expense	The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2020 $ 9,481 2021 8,098 2022 7,547 2023 7,089 Thereafter 8,078

Deferred Acquisition Consider_2

Deferred Acquisition Consideration (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 and December 31, 2018 . December 31, 2019 2018 Beginning balance of contingent payments $ 82,598 $ 119,086 Payments (30,719 ) (54,947 ) Redemption value adjustments (1) 15,451 3,512 Additions - acquisitions and step-up transactions 7,145 14,943 Other (2) 196 4 Ending balance of contingent payments $ 74,671 $ 82,598 Fixed payments 549 1,097 $ 75,220 $ 83,695 (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 cost of services sold and office and general expenses on the Consolidated Statements of Operations. (2) Other primarily consists of translation adjustments. The following table presents the impact to the Company’s statement of operations due to the redemption value adjustments for the contingent deferred acquisition consideration for the twelve months ended December 31, 2019 and 2018 : 2019 2018 (Income) loss attributable to fair value adjustments $ 5,403 $ (3,679 ) Stock-based compensation 10,048 7,191 Redemption value adjustments $ 15,451 $ 3,512

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 : Twelve Months Ended December 31, 2019 Lease Cost: Operating lease cost $ 67,044 Variable lease cost 18,879 Sublease rental income (8,965 ) Total lease cost $ 76,958 Additional information: Cash paid for amounts included in the measurement of lease liabilities for operating leases Operating cash flows $ 69,735 Right-of-use assets obtained in exchange for operating lease liabilities $ 269,801 Weighted average remaining lease term (in years) - Operating leases 5.3 Weighted average discount rate - Operating leases 8.6
Minimum Future Rental Payments	The following table presents minimum future rental payments under the Company’s leases at December 31, 2019 and their reconciliation to the corresponding lease liabilities: Maturity Analysis 2020 $ 69,563 2021 59,216 2022 48,593 2023 43,878 2024 37,260 2025 and thereafter 102,552 Total 361,062 Less: Present value discount (93,240 ) Lease liability $ 267,822

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
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 2019 2018 2017 Service cost $ — $ — $ — Interest cost on benefit obligation 1,640 1,641 1,725 Expected return on plan assets (1,604 ) (1,948 ) (1,830 ) Curtailment and settlements 626 1,039 — Amortization of actuarial (gains) losses 266 258 222 Net periodic benefit cost $ 928 $ 990 $ 117
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 2019 2018 2017 Discount rate 4.42 % 3.83 % 4.32 % Expected return on plan assets 7.00 % 7.00 % 7.40 % 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 2019 2018 2017 Current year actuarial (gain) loss $ 2,917 $ (520 ) $ 1,558 Amortization of actuarial loss (266 ) (258 ) (222 ) Total recognized in other comprehensive (income) loss 2,651 (778 ) 1,336 Total recognized in net periodic benefit cost and other comprehensive loss $ 3,579 $ 212 $ 1,453
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: 2019 2018 2017 Change in benefit obligation: Benefit obligation, Beginning balance $ 37,938 $ 43,750 $ 40,722 Interest Cost 1,640 1,641 1,725 Actuarial (gains) losses 6,127 (3,522 ) 3,088 Benefits paid (2,693 ) (3,931 ) (1,785 ) Benefit obligation, Ending balance 43,012 37,938 43,750 Change in plan assets: Fair value of plan assets, Beginning balance 23,181 27,977 24,482 Actual return on plan assets 4,188 (2,093 ) 3,360 Employer contributions 2,530 1,228 1,920 Benefits paid (2,693 ) (3,931 ) (1,785 ) Fair value of plan assets, Ending balance 27,206 23,181 27,977 Unfunded status $ 15,806 $ 14,757 $ 15,773
Schedule of Amounts Recognized in Balance Sheet	Amounts recognized in the balance sheet at December 31 consist of the following: Pension Benefits 2019 2018 Non-current liability $ 15,806 $ 14,757 Net amount recognized $ 15,806 $ 14,757
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 2019 2018 Accumulated net actuarial losses $ 15,530 $ 12,878 Amount recognized $ 15,530 $ 12,878
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 2019 2018 Discount rate 3.39 % 4.42 % 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, 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 $ — $ — December 31, 2018 Level 1 Level 2 Level 3 Asset Category: Money market fund – Short term investments $ 1,736 $ 1,736 $ — $ — Mutual funds 21,445 21,445 — — Total $ 23,181 $ 23,181 $ — $ —
Schedule of Allocation of Plan Assets	The pension plans weighted-average asset allocation for the years ended December 31, 2019 and 2018 are as follows: Target Allocation Actual Allocation 2019 2019 2018 Asset Category: Equity securities 65.0 % 66.7 % 67.0 % Debt securities 30.0 % 28.6 % 25.5 % Cash/cash equivalents and Short term investments 5.0 % 4.7 % 7.5 % 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 2020 $ 1,885 2021 1,885 2022 1,924 2023 2,198 2024 2,323 Thereafter 11,396

Noncontrolling and Redeemable_2

Noncontrolling and Redeemable Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 were as follows: Noncontrolling Balance, December 31, 2017 $ 11,030 Income attributable to noncontrolling interests 11,785 Distributions made (13,419 ) Other (1) (118 ) Balance, December 31, 2018 $ 9,278 Income attributable to noncontrolling interests 16,156 Distributions made (11,392 ) Other (1) (14 ) Balance, December 31, 2019 $ 14,028 (1) Other primarily consists of cumulative translation adjustments.
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, 2019 2018 2017 Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Transfers from the noncontrolling interest: Increase (decrease) in MDC Partners Inc. paid-in capital for purchase of redeemable noncontrolling interests and noncontrolling interests 1,911 10,140 2,315 Net transfers from noncontrolling interests $ 1,911 $ 10,140 $ 2,315 Change from net income (loss) attributable to MDC Partners Inc. and transfers to noncontrolling interests $ (2,779 ) $ (113,593 ) $ 244,163
Redeemable Noncontrolling Interest [Table Text Block]	The following table presents changes in redeemable noncontrolling interests as of December 31, 2019 and 2018 : Years Ended December 31, 2019 2018 Beginning Balance $ 51,546 $ 62,886 Redemptions (14,530 ) (11,943 ) Granted — — Changes in redemption value (3,163 ) 1,067 Currency translation adjustments 3 (464 ) Other (1) 3,117 — Ending Balance $ 36,973 $ 51,546 (1) Other primarily consists of the redeemable noncontrolling interest balance related to a foreign entity that was classified as held for sale as of December 31, 2018 and reclassified in 2019. See Note 4 of the Notes to the Consolidated Financial Statements included herein for further information.

Share Capital Share Capital (Ta

Share Capital Share Capital (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2018 452,912 $ 9.15 626,940 $ 9.83 Granted 2,738,141 3.08 490,000 2.54 Vested (276,952 ) 3.03 (294,980 ) 12.46 Forfeited (470,300 ) 8.79 (253,000 ) 3.38 Balance at December 31, 2019 2,443,801 $ 3.11 568,960 $ 5.53
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, 2018 111,866 $ 2.23 $ 4.85 Granted — — — Vested — — — Forfeited — — — Exercised — — — Balance at December 31, 2019 111,866 $ 2.23 $ 4.85
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, 2018 250,800 $ 2.35 $ 6.60 Granted 2,425,000 1.04 3.07 Vested — — — Forfeited (350,000 ) 1.31 5.57 Exercised — — — Balance at December 31, 2019 2,325,800 $ 1.14 $ 3.07

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2017 $ (13,656 ) $ 11,702 $ (1,954 ) Other comprehensive income before reclassifications — 6,119 6,119 Amounts reclassified from accumulated other comprehensive income (net of tax expense of $223) 555 — 555 Other comprehensive income 555 6,119 6,674 Balance December 31, 2018 $ (13,101 ) $ 17,821 $ 4,720 Other comprehensive loss 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 loss (1,911 ) (7,078 ) (8,989 ) Balance December 31, 2019 $ (15,012 ) $ 10,743 $ (4,269 )

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
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: 2019 2018 2017 Income (Loss): U.S. $ (16,711 ) $ (68,698 ) $ 48,053 Non-U.S. 38,358 (11,709 ) 39,025 $ 21,647 $ (80,407 ) $ 87,078
Schedule Of Components Of Income Taxes Provision Benefit	The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2019 2018 2017 Current tax provision U.S. federal $ 2,638 $ 444 $ (1,657 ) U.S. state and local 12 2 98 Non-U.S. 2,875 7,584 6,514 5,525 8,030 4,955 Deferred tax provision (benefit): U.S. federal 4,799 (9,315 ) (172,873 ) U.S. state and local 1,183 (2,990 ) (7,775 ) Non-U.S. (974 ) 35,878 7,629 5,008 23,573 (173,019 ) Income tax expense (benefit) $ 10,533 $ 31,603 $ (168,064 )
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: 2019 2018 2017 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ 21,647 $ (80,407 ) $ 87,078 Statutory income tax rate 21.0 % 21.0 % 35.0 % Tax expense (benefit) using U.S. statutory income tax rate 4,546 (16,886 ) 30,477 State and foreign taxes 1,194 (2,988 ) 8,863 Non-deductible stock-based compensation 3,823 1,512 1,441 Other non-deductible expense 709 10,091 (220 ) Change to valuation allowance (2,830 ) 49,482 (103,212 ) Effect of the difference in U.S. federal and local statutory rates 1,422 (152 ) (2,939 ) Impact of tax reform — — (100,472 ) Noncontrolling interests (3,566 ) (2,674 ) (4,413 ) Impact of foreign operations 3,646 1,711 (2,453 ) Adjustment to deferred tax balances — (8,865 ) — Other, net 1,589 372 4,864 Income tax expense (benefit) $10,533 $31,603 $(168,064) Effective income tax rate 48.7% (39.3)% (193.0)%
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: 2019 2018 Deferred tax assets: Capital assets and other $ — $ 905 Net operating loss carry forwards 73,852 70,646 Interest deductions 16,797 8,911 Refinancing charge 669 2,926 Goodwill and intangibles 114,922 123,504 Stock compensation 1,736 2,101 Pension plan 4,414 3,872 Unrealized foreign exchange 11,373 14,645 Capital loss carry forwards 13,081 11,827 Right-of-use assets and accounting reserves 77,824 8,280 Gross deferred tax asset 314,668 247,617 Less: valuation allowance (65,649 ) (68,479 ) Net deferred tax assets 249,019 179,138 Deferred tax liabilities: Lease liabilities $ (67,613 ) $ — Withholding taxes (546 ) — Capital assets (382 ) — Goodwill amortization (98,677 ) (91,726 ) Total deferred tax liabilities (167,218 ) (91,726 ) Net deferred tax asset (liability) $ 81,801 $ 87,412 Disclosed as: Deferred tax assets $ 85,988 $ 92,741 Deferred tax liabilities (4,187 ) (5,329 ) $ 81,801 $ 87,412
Schedule Of Changes In Tax Reserve	If these unrecognized tax benefits were to be recognized, it would affect the Company’s effective tax rate. 2019 2018 2017 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 887 $ 1,433 $ 1,465 Current year positions 275 — 489 Prior period positions — 7 (436 ) Settlements — (314 ) — Lapse of statute of limitations (166 ) (239 ) (85 ) Unrecognized tax benefits - Ending Balance $ 996 $ 887 $ 1,433

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 and 2018 : December 31, 2019 December 31, 2018 Carrying Fair Value Carrying Fair Value Liabilities: 6.50% Senior Notes due 2024 $ 900,000 $ 812,250 $ 900,000 $ 834,750

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Years Ended December 31, 2019 2018 2017 Revenue: Global Integrated Agencies $ 598,184 $ 610,290 $ 688,011 Domestic Creative Agencies 230,718 246,642 277,587 Specialist Communications 180,591 163,367 153,506 Media Services 97,825 121,859 150,198 All Other 308,485 334,045 244,477 Total $ 1,415,803 $ 1,476,203 $ 1,513,779 Segment operating income (loss): Global Integrated Agencies $ 58,933 $ 63,972 $ 60,891 Domestic Creative Agencies 28,254 51 38,221 Specialist Communications 23,822 17,316 19,978 Media Services (5,398 ) (51,169 ) 13,900 All Other 20,397 34,683 39,825 Corporate (45,768 ) (55,157 ) (40,856 ) Total $ 80,240 $ 9,696 $ 131,959 Other Income (expense): Interest expense and finance charges, net $ (64,942 ) $ (67,075 ) $ (64,364 ) Foreign exchange gain (loss) 8,750 (23,258 ) 18,137 Other, net (2,401 ) 230 1,346 Income (loss) before income taxes and equity in earnings of non-consolidated affiliates 21,647 (80,407 ) 87,078 Income tax expense (benefit) 10,533 31,603 (168,064 ) Income (loss) before equity in earnings of non-consolidated affiliates 11,114 (112,010 ) 255,142 Equity in earnings of non-consolidated affiliates 352 62 2,081 Net income (loss) 11,466 (111,948 ) 257,223 Net income attributable to the noncontrolling interest (16,156 ) (11,785 ) (15,375 ) Net income (loss) attributable to MDC Partners Inc. $ (4,690 ) $ (123,733 ) $ 241,848 Years Ended December 31, 2019 2018 2017 Depreciation and amortization: Global Integrated Agencies $ 16,572 $ 21,179 $ 21,206 Domestic Creative Agencies 4,843 5,052 5,143 Specialist Communications 2,577 4,113 4,567 Media Services 3,261 2,693 3,709 All Other 10,208 12,397 7,751 Corporate 868 762 1,098 Total $ 38,329 $ 46,196 $ 43,474 Stock-based compensation: Global Integrated Agencies $ 26,207 $ 8,095 $ 14,666 Domestic Creative Agencies 1,532 2,623 2,301 Specialist Communications 209 372 2,160 Media Services 20 276 614 All Other 1,192 2,391 2,475 Corporate 1,880 4,659 2,134 Total $ 31,040 $ 18,416 $ 24,350 Capital expenditures: Global Integrated Agencies $ 8,223 $ 8,731 $ 18,897 Domestic Creative Agencies 3,044 2,692 4,695 Specialist Communications 1,166 3,553 1,181 Media Services 194 806 3,035 All Other 5,933 4,415 5,127 Corporate 36 67 23 Total $ 18,596 $ 20,264 $ 32,958

Quarterly Results of Operatio_2

Quarterly Results of Operations (Tables)	12 Months Ended
	Dec. 31, 2019
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: 2019 $ 328,791 $ 362,130 $ 342,907 $ 381,975 2018 $ 326,968 $ 379,743 $ 375,830 $ 393,662 Cost of services sold: 2019 $ 237,154 $ 240,749 $ 222,448 $ 260,725 2018 $ 243,030 $ 253,390 $ 238,690 $ 256,088 Net Income (loss): 2019 $ 316 $ 7,333 $ 5,513 $ (1,696 ) 2018 $ (28,519 ) $ 5,951 $ (13,667 ) $ (75,713 ) Net income (loss) attributable to MDC Partners Inc.: 2019 $ (113 ) $ 4,290 $ (1,752 ) $ (7,115 ) 2018 $ (29,416 ) $ 3,406 $ (16,125 ) $ (81,598 ) Income (loss) per common share: Basic 2019 $ (0.04 ) $ 0.01 $ (0.07 ) $ (0.15 ) 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) Diluted 2019 $ (0.04 ) $ 0.01 $ (0.07 ) $ (0.15 ) 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 )

Basis of Presentation and Rec_2

Basis of Presentation and Recent Developments Basis of Presentation and Recent Developments (Details) - USD ($) $ in Millions	Feb. 14, 2020	Feb. 27, 2020	Dec. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Leases not yet commenced, liability			$ 14
Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Leases not yet commenced, liability		$ 115
Subsequent Event | Sloane and Company LLC
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from divestiture of businesses	$ 26
Payment period	2 years
Gain on disposition of business	$ 16

Significant Accounting Polici_3

Significant Accounting Policies - Narrative (Details) - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Other investments	$ 9,854	$ 8,072
Defined contribution plan, expense	$ 11,909	$ 11,136	$ 10,031
Preference shares, authorized (in shares)	145,000	95,000
Preference shares, issued (in shares)	145,000	95,000

New Accounting Pronouncements (

New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease liability	$ 267,822
Operating lease right-of-use asset	$ 223,622		$ 0
Accounting Standards Update 2016-02 - ASC 842
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Lease liability		$ 299,243
Operating lease right-of-use asset		$ 254,245

Acquisitions and Dispositions (

Acquisitions and Dispositions (Details Textual) - USD ($)	Nov. 15, 2019	Apr. 01, 2019	Mar. 08, 2019	Dec. 31, 2018	Dec. 31, 2019
Business Acquisition [Line Items]
Deferred acquisition consideration				$ 83,695,000	$ 75,220,000
Laird - Partners [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)	35.00%
Aggregate purchase price	$ 2,389,000
Closing cash payment	1,588,000
Deferred acquisition consideration	801,000
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination	6,005,000
Business acquisitions and step-up transactions, net of tax	(5,045,000)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value	$ 2,656,000
Hunter PR LLC [Member]
Business Acquisition [Line Items]
Remaining ownership interest acquired (percent)		35.00%
Aggregate purchase price		$ 10,234,000
Closing cash payment		3,890,000
Deferred acquisition consideration		6,344,000
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination		20,178,000
Business acquisitions and step-up transactions, net of tax		(9,486,000)
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value		$ 745,000
Aggregate 2018 Acquisitions [Member]
Business Acquisition [Line Items]
Aggregate purchase price				56,463,000
Deferred acquisition consideration				16,174,000
Business acquisitions and step-up transactions, net of tax				(9,790,000)
Granted				4,975,000
Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value				15,411,000
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable				$ 1,011,561
Kingsdale Partners LP [Member]
Business Acquisition [Line Items]
Proceeds from divestiture of businesses			$ 50,000,000
Loss on disposition of business			$ (3,000,000)

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Services	$ 381,975	$ 342,907	$ 362,130	$ 328,791	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 1,415,803	$ 1,476,203	$ 1,513,779
United States
Disaggregation of Revenue [Line Items]
Services									1,116,045	1,153,191	1,172,364
Canada
Disaggregation of Revenue [Line Items]
Services									105,067	124,001	123,093
Other
Disaggregation of Revenue [Line Items]
Services									194,691	199,011	218,322
Food & Beverage
Disaggregation of Revenue [Line Items]
Services									280,094	313,368	313,786
Retail
Disaggregation of Revenue [Line Items]
Services									148,851	152,552	178,152
Consumer Products
Disaggregation of Revenue [Line Items]
Services									167,324	162,524	162,307
Communications
Disaggregation of Revenue [Line Items]
Services									184,870	178,410	208,701
Automotive
Disaggregation of Revenue [Line Items]
Services									78,985	88,807	127,023
Technology
Disaggregation of Revenue [Line Items]
Services									118,169	104,479	99,325
Healthcare
Disaggregation of Revenue [Line Items]
Services									102,221	127,547	124,261
Financials
Disaggregation of Revenue [Line Items]
Services									112,351	110,069	104,713
Transportation and Travel/Lodging
Disaggregation of Revenue [Line Items]
Services									88,958	86,419	56,955
Other
Disaggregation of Revenue [Line Items]
Services									$ 133,980	$ 152,028	$ 138,556

Revenue - Contract Assets and L

Revenue - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Unbilled service fees	$ 66,119	$ 64,362
Unbilled outside vendor costs, billable to clients	30,133	42,369
Advance billings	171,742	$ 138,505
Deferred Revenue, Additions	33,237
Revenue recognized	$ 121,659

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Net loss attributable to MDC Partners Inc.	$ (7,115)	$ (1,752)	$ 4,290	$ (113)	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ (4,690)	$ (123,733)	$ 241,848
Numerator
Net income (loss) attributable to MDC Partners Inc. common shareholders									(16,994)	(132,088)	205,594
Adjustment to Net Income, Allocated to Convertible Shares									0	0	106
Income (Loss) from Continuing Operations Attributable to Parent, Diluted									$ (16,994)	$ (132,088)	$ 205,700
Denominator
Denominator for basic income (loss) per common share - weighted average common shares									69,132,100	57,218,994	55,255,797
Weighted Average Number Diluted Shares Outstanding Adjustment									0	0	225,989
Denominator for diluted income (loss) per common share - adjusted weighted shares and assumed conversions									69,132,100	57,218,994	55,481,786
Earnings per share, basic									$ (0.25)	$ (2.31)	$ 3.72
Earnings per share, diluted									$ (0.25)	$ (2.31)	$ 3.71
Series 4 Convertible Preferred Stock | Convertible Preference Shares
Numerator
Accretion on and net income allocated to convertible preference shares									$ 12,304	$ 8,355	$ 6,352
Net Income Allocated to Convertible Shares									$ 0	$ 0	$ (29,902)
Denominator
Antidilutive securities excluded from computation of earnings per share (shares)									5,450,426,000	1,442,518,000	0

Income (Loss) Per Common Shar_3

Income (Loss) Per Common Share (Details Textual) - shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
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)	135,386	1,012,637	1,443,921
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)	5,450,426,000	1,442,518,000	0
Shares outstanding (shares)	145,000,000	95,000,000	95,000,000	0
Convertible preferred stock, common shares issuable upon conversion (shares)	26,656,285	10,970,714	10,135,244

Fixed Assets - Schedule of Fixe

Fixed Assets - Schedule of Fixed Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Fixed assets, cost	$ 210,633	$ 216,735
Fixed assets, accumulated depreciation	129,579	128,546
Fixed assets, net book value	81,054	88,189
Computers, furniture and fixtures
Property, Plant and Equipment [Line Items]
Fixed assets, cost	93,224	100,276
Fixed assets, accumulated depreciation	69,687	73,060
Fixed assets, net book value	23,537	27,216
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Fixed assets, cost	117,409	116,459
Fixed assets, accumulated depreciation	59,892	55,486
Fixed assets, net book value	$ 57,517	$ 60,973

Fixed Assets - Narrative (Detai

Fixed Assets - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 25,133	$ 27,111	$ 23,873

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Beginning Balance	$ 740,955	$ 835,935
Acquired goodwill	1,025	37,592
Impairment loss recognized	(4,099)	(74,560)
Transfer of goodwill between segments	0	0
Transfer of goodwill to asset held for sale	0	(45,224)
Foreign currency translation	2,793	(12,788)
Ending Balance	740,674	740,955
Media Services
Goodwill [Roll Forward]
Beginning Balance	111,346	160,057
Acquired goodwill	0	0
Impairment loss recognized	0	(52,041)
Transfer of goodwill between segments	(24,119)	3,773
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	0	(443)
Ending Balance	87,227	111,346
All Other [Domain]
Goodwill [Roll Forward]
Beginning Balance	154,171	201,121
Acquired goodwill	1,025	32,776
Impairment loss recognized	(4,099)	(4,691)
Transfer of goodwill between segments	(4,206)	(22,920)
Transfer of goodwill to asset held for sale	0	(45,224)
Foreign currency translation	1,440	(6,891)
Ending Balance	148,331	154,171
Global Integrated Agencies
Goodwill [Roll Forward]
Beginning Balance	353,155	359,071
Acquired goodwill	0	0
Impairment loss recognized	0	(17,828)
Transfer of goodwill between segments	(85,766)	17,081
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	775	(5,169)
Ending Balance	268,164	353,155
Domestic Creative Agencies
Goodwill [Roll Forward]
Beginning Balance	38,780	36,980
Acquired goodwill	0	0
Impairment loss recognized	0	0
Transfer of goodwill between segments	119,097	2,066
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	402	(266)
Ending Balance	158,279	38,780
Specialist Communications [Member]
Goodwill [Roll Forward]
Beginning Balance	83,503	78,706
Acquired goodwill	0	4,816
Impairment loss recognized	0	0
Transfer of goodwill between segments	(5,006)	0
Transfer of goodwill to asset held for sale	0	0
Foreign currency translation	176	(19)
Ending Balance	$ 78,673	$ 83,503

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Intangibles:
Trademarks (indefinite life)	$ 14,600	$ 14,600
Intangible assets, gross	101,506	122,386
Less accumulated amortization	(46,613)	(54,621)
Total intangible assets-net	54,893	67,765
Other Intangible Assets
Intangibles:
Intangible assets, gross	28,695	31,421
Less accumulated amortization	(13,942)	(12,441)
Intangible assets, net	14,753	18,980
Customer Relationships
Intangibles:
Intangible assets, gross	58,211	76,365
Less accumulated amortization	(32,671)	(42,180)
Intangible assets, net	$ 25,540	$ 34,185

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Textual (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)reportable_segment	Dec. 31, 2018USD ($)reportable_segment	Dec. 31, 2017USD ($)reportable_segment
Goodwill [Line Items]
Goodwill and other asset impairment	$ 5,875	$ 56,732	$ 7,819	$ 80,057	$ 4,415
Number of Reporting Units | reportable_segment				3	2
Goodwill, Impairment Loss			4,099	$ 74,560
Goodwill, impaired, accumulated impairment loss	$ 177,304	$ 173,205	$ 177,304	173,205
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			8 years
Amortization Of Intangible Assets, Finite Lived			$ 11,828	$ 17,290	$ 17,125
Customer Relationships
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			7 years
Other Intangible Assets
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life			9 years
Global Integrated Agencies
Goodwill [Line Items]
Number of Reporting Units | reportable_segment				1	1
Impairment of Intangible Assets (Excluding Goodwill)				$ 3,180
Media Services
Goodwill [Line Items]
Number of Reporting Units | reportable_segment				1	1
All Other
Goodwill [Line Items]
Number of Reporting Units | reportable_segment			1

Goodwill and Intangible Asset_5

Goodwill and Intangible Assets - Schedule of Finite-lived Intangible Assets Amortization Expense (Details) $ in Thousands	Dec. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
2020	$ 9,481
2021	8,098
2022	7,547
2023	7,089
Thereafter	$ 8,078

Deferred Acquisition Consider_3

Deferred Acquisition Consideration (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			$ 82,598	$ 119,086
Payments			30,719	54,947
Redemption value adjustments			15,451	3,512
Additions			7,145	14,943
Foreign translation adjustment			196	4
Ending balance of contingent payments	$ 74,671	$ 82,598	74,671	82,598
Deferred acquisition consideration	75,220	83,695	75,220	83,695
Stock-based compensation			10,048	7,191
Fixed payments
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Deferred acquisition consideration	549	1,097	549	1,097
Contingent Payment
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
(Income) loss attributable to fair value adjustments	$ 9,030	$ (8,979)	$ 5,403	$ (3,679)

Leases - Lease Costs and Other

Leases - Lease Costs and Other Quantitative Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Operating lease cost	$ 67,044	$ 65	$ 64,086
Variable lease cost	18,879
Sublease rental income	(8,965)	$ (3,671)	$ (2,797)
Total lease cost	76,958
Operating cash flows	69,735
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 269,801
Weighted average remaining lease term (in years) - Operating leases	5 years 3 months 23 days
Weighted average discount rate - Operating leases	8.60%

Leases - Minimum Future Rental

Leases - Minimum Future Rental Payments (Details) $ in Thousands	Dec. 31, 2019USD ($)
Leases [Abstract]
2020	$ 69,563
2021	59,216
2022	48,593
2023	43,878
2024	37,260
Thereafter	102,552
Total	361,062
Less: Present value discount	(93,240)
Lease liability	$ 267,822

Leases - Additional Information

Leases - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Abstract]
Leases not yet commenced, liability	$ 14,000
Impairment of right-of-use asset	3,700
Operating lease cost	67,044	$ 65	$ 64,086
Sublease rental income	$ 8,965	$ 3,671	$ 2,797

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Mar. 23, 2016
Debt [Line Items]
Revolving credit agreement	$ 0	$ 68,143
Debt issuance costs	(12,370)	(14,036)
Debt, Long-term and Short-term, Combined Amount, Total	887,630	954,107
6.50% Notes due 2024
Debt [Line Items]
Senior Notes	$ 900,000	$ 900,000	$ 900,000

Debt (Details Textual)

Debt (Details Textual)	12 Months Ended
	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2020	Mar. 12, 2019USD ($)	May 03, 2016USD ($)	Mar. 23, 2016USD ($)
Debt [Line Items]
Interest Expense, Debt	$ 62,210,000	$ 64,420,000	$ 62,001,000
Amortization of Debt Issuance Costs and Discounts	3,346,000	3,193,000	$ 3,022,000
Amount of letters of credit outstanding	4,836,000	4,701,000
6.50% Notes due 2024
Debt [Line Items]
Senior Notes	$ 900,000,000	$ 900,000,000					$ 900,000,000
Wells Fargo Capital Finance, LLC | Revolving Credit Facility [Member]
Debt [Line Items]
Maximum borrowing capacity						$ 325,000,000
Ratio of Indebtedness to Net Capital						5.5
Senior Notes | 6.50% Notes due 2024
Debt [Line Items]
Interest rate, stated percentage	6.50%						6.50%
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] | Amendment, Credit Agreement [Member]
Debt [Line Items]
Maximum borrowing capacity	$ 250,000,000				$ 250,000,000
Ratio of Indebtedness to Net Capital					6.25
Forecast | Line of Credit [Member] | Amendment, Credit Agreement [Member]
Debt [Line Items]
Ratio of Indebtedness to Net Capital				5.5
Non-Prime Rate and Prime Rate on European Advances [Member] | Wells Fargo Capital Finance, LLC | Revolving Credit Facility [Member]
Debt [Line Items]
Interest rate, stated percentage					0.75%
Base Rate [Member] | Wells Fargo Capital Finance, LLC | Revolving Credit Facility [Member]
Debt [Line Items]
Interest rate, stated percentage					1.50%

Employee Benefit Plans - Sched

Employee Benefit Plans - Schedule of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost on benefit obligation	1,640	1,641	1,725
Expected return on plan assets	(1,604)	(1,948)	(1,830)
Curtailment and settlements	626	1,039	0
Amortization of actuarial losses	266	258	222
Net periodic benefit cost	$ 928	$ 990	$ 117

Employee Benefit Plans - Sch_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	4.42%	3.83%	4.32%
Expected return on plan assets	7.00%	7.00%	7.40%

Employee Benefit Plans - Sch_3

Employee Benefit Plans - Schedule of Defined Benefit Plan Amounts in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Current year actuarial (gain) loss	$ 2,917	$ (520)	$ 1,558
Amortization of actuarial loss	(266)	(258)	(222)
Total recognized in other comprehensive (income) loss	2,651	(778)	1,336
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ 3,579	$ 212	$ 1,453

Employee Benefit Plans - Sch_4

Employee Benefit Plans - Schedule of Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligation:
Benefit obligation, Beginning balance	$ 37,938	$ 43,750	$ 40,722
Interest Cost	1,640	1,641	1,725
Actuarial (gains) losses	6,127	(3,522)	3,088
Benefits paid	(2,693)	(3,931)	(1,785)
Benefit obligation, Ending balance	43,012	37,938	43,750
Change in plan assets:
Fair value of plan assets, Beginning balance	23,181	27,977	24,482
Actual return on plan assets	4,188	(2,093)	3,360
Employer contributions	2,530	1,228	1,920
Benefits paid	(2,693)	(3,931)	(1,785)
Fair value of plan assets, Ending balance	27,206	23,181	27,977
Unfunded status	$ 15,806	$ 14,757	$ 15,773

Employee Benefit Plans - Sch_5

Employee Benefit Plans - Schedule of Amounts Recognized in Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts recognized in the balance sheet consist of:
Non-current liability	$ 15,806	$ 14,757	$ 15,773
Net amount recognized	$ 15,806	$ 14,757

Employee Benefit Plans - Sch_6

Employee Benefit Plans - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Accumulated net actuarial losses	$ 15,530	$ 12,878
Amount recognized	$ 15,530	$ 12,878

Employee Benefit Plans - Sch_7

Employee Benefit Plans - Schedule of Assumptions Used to Determine Benefit Obligation (Details)	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Discount rate	3.39%	4.42%

Employee Benefit Plans - Sch_8

Employee Benefit Plans - Schedule of Changes in Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 27,206	$ 23,181	$ 27,977	$ 24,482
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,931	21,445
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,275	1,736
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27,206	23,181
Fair Value, Inputs, Level 1 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	25,931	21,445
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,275	1,736
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 - Sch_9

Employee Benefit Plans - Schedule of Allocation of Plan Assets (Details)	Dec. 31, 2019	Dec. 31, 2018
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	4.70%	7.50%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	65.00%
Actual allocation	66.70%	67.00%
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Target allocation	30.00%
Actual allocation	28.60%	25.50%

Employee Benefit Plans - Sc_10

Employee Benefit Plans - Schedule of Expected Benefit Payments (Details) $ in Thousands	Dec. 31, 2019USD ($)
Estimated Future Benefit Payments for FYE 12/31
2020	$ 1,885
2021	1,885
2022	1,924
2023	2,198
2024	2,323
Thereafter	$ 11,396

Employee Benefit Plans - Textu

Employee Benefit Plans - Textual (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Estimate of net actuarial losses reclassified from AOCI in the next fiscal year		$ (1,911)	$ 555
Current employer pension plan contributions		2,530	$ 1,228	$ 1,920
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	$ 340
Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Expected pension plan contribution		$ 2,344

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, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncontrolling Interest [Abstract]
Beginning balance	$ 9,278	$ 11,030
Income attributable to noncontrolling interests	16,156	11,785	$ 15,375
Distributions made	(11,392)	(13,419)	(8,865)
Other	(14)	(118)
Ending balance	$ 14,028	$ 9,278	$ 11,030

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.	$ (7,115)	$ (1,752)	$ 4,290	$ (113)	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ (4,690)	$ (123,733)	$ 241,848
Business acquisitions and step-up transactions, net of tax									1,911	25,550	(9,650)
Change from net income (loss) attributable to MDC Partners Inc. and transfers to noncontrolling interests									2,779	113,593	(244,163)
MDC Partners Inc. Shareholders' Deficit
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.										(123,733)	241,848
Business acquisitions and step-up transactions, net of tax									$ 1,911	$ 10,140	$ 2,315

Noncontrolling and Redeemable_5

Noncontrolling and Redeemable Noncontrolling Interests - Changes in Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Noncontrolling Interest [Abstract]
Beginning Balance	$ 51,546	$ 62,886
Redemptions	(14,530)	(11,943)
Granted	0	0
Changes in redemption value	(3,163)	1,067
Currency translation adjustments	3	(464)
Other	3,117	0
Ending Balance	$ 36,973	$ 51,546

Noncontrolling and Redeemable_6

Noncontrolling and Redeemable Noncontrolling Interests (Details Textual) - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 36,973,000	$ 51,546,000	$ 62,886,000
Vesting over period [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	18,891,000
Termination, disability, or death [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	15,336,000
Acquisition Value in excess of Redemption Value [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 2,746,000

Commitments, Contingencies an_2

Commitments, Contingencies and Guarantees (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Amount of letters of credit outstanding	$ 4,836	$ 4,701

Share Capital - Textual (Detail

Share Capital - Textual (Details)	Mar. 14, 2019USD ($)$ / sharesshares	Jun. 30, 2019USD ($)	Sep. 30, 2018	Dec. 31, 2019USD ($)vote$ / sharesshares	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)shares	Sep. 30, 2019USD ($)	Mar. 07, 2017$ / shares
Share Capital [Line Items]
Issuance of common and convertible preference shares				$ 98,620,000		$ 90,220,000
Convertible preference shares, 145,000 authorized, issued and outstanding at December 31, 2019 and 95,000 at December 31, 2018				152,746,000	$ 90,123,000
Expenses for convertible preference shares					(97,000)
Allocated Share-based Compensation Expense				2,000	6,000	5,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense				643,000	472,000	1,401,000
Proceeds from Stock Options Exercised						0
Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Proceeds from issuance of common and convertible preference shares, net of issuance costs				$ 98,620,000	$ 0	$ 90,220,000
Convertible Preference Shares
Share Capital [Line Items]
Proceeds from issuance of common and convertible preference shares, net of issuance costs	$ 98,620,000
Convertible Preference Shares | Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Preferred Stock, Liquidation Preference Per Share | $ / shares									$ 1,000
Preferred Stock, Conversion Price Per Preference Share | $ / shares	$ 7.42								$ 10
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Accretion Rate, Preference Per Share | $ / shares				$ 8.17	$ 7.55
Preferred Stock, Accretion of Redemption Discount				$ 9,043,000	$ 8,355,000
Preferred Stock, Liquidation Preference, Value				$ 119,000
Shares outstanding (shares) | shares				145,000,000	95,000,000	95,000,000	0
Expenses for convertible preference shares					$ (97,000)
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]
Stock Issued During Period, Shares, Issued For Services, Convertible Preferred Shares | shares	50,000
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 Preference 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				$ 6.96
Preferred Stock, Accretion of Redemption Discount		$ 3,261,000
Preferred Stock, Liquidation Preference, Value								$ 53,000
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
Shares outstanding (shares) | shares				72,150,854	57,517,568
Common stock, voting rights, number of votes per share | vote				1
Common Shares | Common Class B
Share Capital [Line Items]
Shares outstanding (shares) | shares				3,749	3,755	3,755
Common stock, voting rights, number of votes per share | vote				20
Contingent Consideration, Liability Settlements [Domain] | Convertible Preference Shares | Series 4 Convertible Preferred Stock
Share Capital [Line Items]
Issuance of common and convertible preference shares						$ 90,220,000
Contingent Consideration, Liability Settlements [Domain] | Convertible Preference Shares | Series 6 Convertible Preferred Shares [Member]
Share Capital [Line Items]
Issuance of common and convertible preference shares	$ 62,623,000
Employee Stock Incentive Plan [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized | shares				15,650,000
Employee Stock Option [Member]
Share Capital [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Option, Nonvested, Weighted Average Exercise Price | $ / shares					$ 2.23	$ 2.23
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized				$ 150,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition				2 years
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term					4 years 10 months 24 days
Vested (in shares) | shares					0
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, Outstanding, Weighted Average Remaining Contractual Term					2 years
ERROR in label resolution.						$ 125,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period | shares				0	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value				$ 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					$ 4,517,000	$ 3,583,000	$ 7,316,000
Stock Appreciation Rights (SARs) [Member]
Share Capital [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options				$ 1,298,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value | $ / shares					$ 1.14	$ 2.35
Weighted average grant date fair value, granted (in dollars per share) | $ / shares					$ 1.04	$ 2.35
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition				1 year 2 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term				5 years		5 years
Vested (in shares) | shares					0
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate						1.70%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate						46.20%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate					0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term				1 year 2 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period | shares				0	350,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding				$ 885,000
Performance Shares [Member] | Employee Stock 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				$ 3,110	$ 9,150
Weighted average grant date fair value, granted (in dollars per share) | $ / shares				$ 3,080	$ 9.17
Granted (in shares) | shares				2,738,141,000		0
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized					$ 5,341,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition					2 years 1 month 6 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				2 years 1 month 6 days
Time Based Awards [Member] | Employee Stock 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				$ 5,530	$ 9,830
Weighted average grant date fair value, granted (in dollars per share) | $ / shares				$ 2,540	$ 7.38	$ 8.98
Granted (in shares) | shares				490,000,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized					$ 919,000
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition					1 year 11 months 5 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 11 months 5 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) - Employee Stock Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	452,912,000
Granted (in shares)	2,738,141,000		0
Vested (in shares)	276,952,000
Forfeited (in shares)	470,300,000
Ending balance (in shares)	2,443,801,000	452,912,000
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 9,150
Weighted average grant date fair value, granted (in dollars per share)	3,080	$ 9.17
Weighted average grant date fair value, vested (in dollars per share)	3,030
Weighted average grant date fair value, forfeited (in dollars per share)	8,790
Weighted average grant date fair value, ending balance (in dollars per share)	$ 3,110	$ 9,150
Time Based Awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	626,940,000
Granted (in shares)	490,000,000
Vested (in shares)	294,980,000
Forfeited (in shares)	253,000,000
Ending balance (in shares)	568,960,000	626,940,000
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 9,830
Weighted average grant date fair value, granted (in dollars per share)	2,540	$ 7.38	$ 8.98
Weighted average grant date fair value, vested (in dollars per share)	12,460
Weighted average grant date fair value, forfeited (in dollars per share)	3,380
Weighted average grant date fair value, ending balance (in dollars per share)	$ 5,530	$ 9,830

Share Capital - Schedule of S_2

Share Capital - Schedule of Shared Based Compensation, Stock Options (Details) - Employee Stock Option [Member] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	111,866	111,866
Granted (in shares)		0
Vested (in shares)		0
Forfeited (in shares)	0	0
Exercised (in shares)		0
Ending balance (in shares)		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, vested (in dollars per share)		0
Weighted average grant date fair value, forfeited (in dollars per share)		0
Weighted average grant date fair value, exercised (in dollars per share)		0
Weighted average grant date fair value, ending balance (in dollars per share)		2.23
Weighted average exercise price, beginning balance (in dollars per share)	$ 4.85	4.85
Weighted average exercise price, granted (in dollars per share)		0
Weighted average exercise price, vested (in dollars per share)		0
Weighted average exercise price, forfeited (in dollars per share)		0
Weighted average exercise price, exercised (in dollars per share)		0
Weighted average exercise price, ending balance (in dollars per share)		$ 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] - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning balance (in shares)	2,325,800	250,800
Ending balance (in shares)		2,325,800	250,800
Weighted average grant date fair value, beginning balance (in dollars per share)	$ 1.14	$ 2.35
Weighted average grant date fair value, ending balance (in dollars per share)		1.14	$ 2.35
Weighted average exercise price, beginning balance (in dollars per share)	$ 3.07	6.60
Weighted average exercise price, ending balance (in dollars per share)		$ 3.07	6.60
Vested (in shares)		0
Weighted average grant date fair value, granted (in dollars per share)		$ 1.04	$ 2.35
Weighted average exercise price, vested (in dollars per share)		$ 3.07
Granted (in shares)		2,425,000
Weighted average grant date fair value, vested (in dollars per share)		$ 0
Weighted average exercise price, granted (in dollars per share)		$ 0
Exercised (in shares)		0
Weighted average grant date fair value, forfeited (in dollars per share)		$ 1.31
Weighted average exercise price, exercised (in dollars per share)		$ 5.57
Forfeited (in shares)	0	(350,000)
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, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Defined benefit pension, balance January 1	$ (13,101)	$ (13,656)
Foreign currency translation, balance January 1	17,821	11,702
Total, balance January 1	4,720	(1,954)
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	(7,078)	6,119
Total, other comprehensive income (loss) before reclassifications	(7,078)	6,119
Amounts reclassified from accumulated other comprehensive income (loss)	(1,911)	555
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Total, amounts reclassified from accumulated other comprehensive income (loss)	(1,911)	555
Defined benefit pension, other comprehensive income (loss)	(1,911)	555	$ (1,336)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent	(7,078)	6,119
Total, other comprehensive income (loss)	(8,989)	6,674
Defined benefit pension, balance December 31	(15,012)	(13,101)	(13,656)
Foreign currency translation, balance December 31	10,743	17,821	11,702
Total, balance December 31	$ (4,269)	$ 4,720	$ (1,954)

Income Taxes - Schedule of Inc

Income Taxes - Schedule of Income before income tax, Domestic and Foreign (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	$ 21,647	$ (80,407)	$ 87,078
Domestic Tax Authority
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	(16,711)	(68,698)	48,053
Non-U.S.
Income Tax [Line Items]
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	$ 38,358	$ (11,709)	$ 39,025

Income Taxes - Schedule of Com

Income Taxes - Schedule of Components of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax [Line Items]
Current tax provision	$ 5,525	$ 8,030	$ 4,955
Deferred tax provision (benefit)	5,008	23,573	(173,019)
Income tax provision (benefit)	10,533	31,603	(168,064)
United States Federal
Income Tax [Line Items]
Current tax provision	2,638	444	(1,657)
Deferred tax provision (benefit)	4,799	(9,315)	(172,873)
United States And Local
Income Tax [Line Items]
Current tax provision	12	2	98
Deferred tax provision (benefit)	1,183	(2,990)	(7,775)
Foreign
Income Tax [Line Items]
Current tax provision	2,875	7,584	6,514
Deferred tax provision (benefit)	$ (974)	$ 35,878	$ 7,629

Income Taxes - Schedule of Eff

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest	$ 21,647	$ (80,407)	$ 87,078
Tax expense (benefit) using U.S. statutory income tax rate	4,546	(16,886)	30,477
State and foreign taxes	1,194	(2,988)	8,863
Non-deductible stock-based compensation	3,823	1,512	1,441
Other non-deductible expense	709	10,091	(220)
Change to valuation allowance	(2,830)	49,482	(103,212)
Effect of the difference in U.S. federal and local statutory rates	1,422	(152)	(2,939)
Impact of tax reform	0	0	(100,472)
Noncontrolling interests	(3,566)	(2,674)	(4,413)
Impact of foreign operations	3,646	1,711	(2,453)
Adjustment to deferred tax balances	0	(8,865)	0
Other, net	1,589	372	4,864
Income tax provision (benefit)	$ 10,533	$ 31,603	$ (168,064)
Effective income tax rate	48.70%	(39.30%)	(193.00%)

Income Taxes - Schedule of Def

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Capital assets and other	$ 0	$ 905
Net operating loss carry forwards	73,852	70,646
Interest deductions	16,797	8,911
Refinancing charge	669	2,926
Goodwill and intangibles	114,922	123,504
Stock compensation	1,736	2,101
Pension plan	4,414	3,872
Unrealized foreign exchange	11,373	14,645
Capital loss carry forwards	13,081	11,827
Accounting reserves	77,824	8,280
Gross deferred tax asset	314,668	247,617
Less: valuation allowance	(65,649)	(68,479)
Net deferred tax assets	249,019	179,138
Deferred tax liabilities:
Lease liabilities	(67,613)
Withholding taxes	(546)	0
Capital assets	(382)	0
Goodwill amortization	(98,677)	(91,726)
Total deferred tax liabilities	(167,218)	(91,726)
Deferred Tax Assets, Net	81,801	87,412
Disclosed as:
Deferred tax assets	85,988	92,741
Deferred tax liabilities	$ (4,187)	$ (5,329)

Income Taxes - Schedule of Cha

Income Taxes - Schedule of Changes in Tax Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Reserve [Roll Forward]
Beginning Balance	$ 887	$ 1,433	$ 1,465
Current year positions	275	0	489
Prior period positions	0	7	(436)
Settlements	0	(314)	0
Lapse of statute of limitations	(166)	(239)	(85)
Ending Balance	$ 996	$ 887	$ 1,433

Income Taxes - Textual (Detail

Income Taxes - Textual (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2015
Income Tax [Line Items]
Indefinite loss carryforwards		$ 205,050,000		$ 205,050,000
Valuation allowance	$ 65,649,000	68,479,000	$ 65,649,000	68,479,000
Valuation allowance, deferred tax asset, increase (decrease), amount	2,830,000	(49,447,000)
Undistributed earnings no longer subject to reinvestment assertion	5,000,000		5,000,000
Tax expense related to estimated tax costs associated with change in assertion			546,000
Income tax expense (benefit)			10,533,000	31,603,000	$ (168,064,000)
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest			21,647,000	(80,407,000)	87,078,000
Income taxes receivable		5,025,000		5,025,000	4,388,000
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount			709,000	10,091,000	(220,000)
Non-deductible stock-based compensation			3,823,000	1,512,000	1,441,000
Change to valuation allowance			(2,830,000)	49,482,000	(103,212,000)
Impact of tax reform			1,422,000	(152,000)	(2,939,000)
Taxes payable		11,722,000		11,722,000	10,045,000
Unrecognized tax benefits	1,107,000	973,000	1,107,000	973,000
Unrecognized tax benefits, income tax penalties and interest accrued	111,000	87,000	111,000	87,000
United States Federal
Income Tax [Line Items]
Operating loss carryforwards		45,094,000		45,094,000
United States
Income Tax [Line Items]
Indefinite loss carryforwards		106,329,000		106,329,000
Non-U.S.
Income Tax [Line Items]
Operating loss carryforwards		146,037,000		146,037,000
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest			38,358,000	(11,709,000)	$ 39,025,000
Canada
Income Tax [Line Items]
Indefinite loss carryforwards		$ 98,721,000		$ 98,721,000
State and Local Jurisdiction
Income Tax [Line Items]
Operating loss carryforwards	176,174,000		176,174,000
Minimum
Income Tax [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	200,000		200,000
Maximum
Income Tax [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 300,000		$ 300,000
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset
Income Tax [Line Items]
Decrease in overall valuation allowance						$ (2,830,000)

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($) $ in Thousands	Jan. 01, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Oct. 31, 2019
Related Party Transaction [Line Items]
Sublease rental income		$ 8,965	$ 3,671	$ 2,797
Stagwell Subsidiary [Member] | Services Provided By Subisidiary [Member]
Related Party Transaction [Line Items]
Accounts Payable, Related Parties					$ 655
Due to Related Parties		$ 393
Other Company [Member] | Board of Directors Chairman [Member] | Subsequent Event [Member]
Related Party Transaction [Line Items]
Sublease rental income	$ 350

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Goodwill, Impairment Loss			$ 4,099	$ 74,560
Goodwill and other asset impairment	$ 5,875	$ 56,732	7,819	80,057	$ 4,415
Impairment of right-of-use asset			3,700
6.50% Notes due 2024 | Fair Value, Inputs, Level 1 | Senior Notes
Liabilities:
Long term debt, Carrying Amount	900,000	900,000	900,000	900,000
Long term debt, Fair Value	$ 812,250	$ 834,750	$ 812,250	$ 834,750

Segment Information (Details 1)

Segment Information (Details 1)	3 Months Ended								12 Months Ended
	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2019USD ($)reportable_segmentoperating_segment	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment									4
Revenue	$ 381,975,000	$ 342,907,000	$ 362,130,000	$ 328,791,000	$ 393,662,000	$ 375,830,000	$ 379,743,000	$ 326,968,000	$ 1,415,803,000	$ 1,476,203,000	$ 1,513,779,000
Segment operating income (loss)									80,240,000	9,696,000	131,959,000
Interest expense and finance charges									(64,942,000)	(67,075,000)
Interest Expense, Other											64,364,000
Foreign exchange gain (loss)	4,349,000				(13,324,000)				8,750,000	(23,258,000)	18,137,000
Other, net									(2,401,000)	230,000	1,346,000
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates									21,647,000	(80,407,000)	87,078,000
Income tax expense (benefit)									10,533,000	31,603,000	(168,064,000)
Income (loss) before equity in earnings of non-consolidated affiliates									11,114,000	(112,010,000)	255,142,000
Equity in earnings of non-consolidated affiliates									352,000	62,000	2,081,000
Net income (loss)									11,466,000	(111,948,000)	257,223,000
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,696,000)	5,513,000	7,333,000	316,000	(75,713,000)	(13,667,000)	5,951,000	(28,519,000)			257,223,000
Net income attributable to the noncontrolling interest									(16,156,000)	(11,785,000)	(15,375,000)
Net income (loss) attributable to MDC Partners Inc.	(7,115,000)	$ (1,752,000)	$ 4,290,000	$ (113,000)	(81,598,000)	$ (16,125,000)	$ 3,406,000	$ (29,416,000)	(4,690,000)	(123,733,000)	241,848,000
Depreciation and amortization									38,329,000	46,196,000	43,474,000
Stock-based compensation	$ 18,408,000				$ 1,534,000				31,040,000	18,416,000	24,350,000
Capital expenditures									$ 18,596,000	20,264,000	32,958,000
Global Integrated Agencies
Segment Reporting Information [Line Items]
Number of operating segments | operating_segment									4
Revenue									$ 598,184,000	610,290,000	688,011,000
Segment operating income (loss)									58,933,000	63,972,000	60,891,000
Depreciation and amortization									16,572,000	21,179,000	21,206,000
Stock-based compensation									26,207,000	8,095,000	14,666,000
Capital expenditures									$ 8,223,000	8,731,000	18,897,000
Domestic Creative Agencies
Segment Reporting Information [Line Items]
Number of operating segments | operating_segment									7
Revenue									$ 230,718,000	246,642,000	277,587,000
Segment operating income (loss)									28,254,000	51,000	38,221,000
Depreciation and amortization									4,843,000	5,052,000	5,143,000
Stock-based compensation									1,532,000	2,623,000	2,301,000
Capital expenditures									$ 3,044,000	2,692,000	4,695,000
Specialized Communications
Segment Reporting Information [Line Items]
Number of operating segments | operating_segment									4
Revenue									$ 180,591,000	163,367,000
Segment operating income (loss)									23,822,000	17,316,000
Depreciation and amortization									2,577,000	4,113,000	4,567,000
Stock-based compensation									209,000	372,000	2,160,000
Capital expenditures									1,166,000	3,553,000	1,181,000
Specialist Communications [Member]
Segment Reporting Information [Line Items]
Revenue											153,506,000
Segment operating income (loss)											19,978,000
Media Services
Segment Reporting Information [Line Items]
Revenue									97,825,000	121,859,000	150,198,000
Segment operating income (loss)									(5,398,000)	(51,169,000)	13,900,000
Depreciation and amortization									3,261,000	2,693,000	3,709,000
Stock-based compensation									20,000	276,000	614,000
Capital expenditures									194,000	806,000	3,035,000
All Other
Segment Reporting Information [Line Items]
Revenue									308,485,000	334,045,000	244,477,000
Segment operating income (loss)									20,397,000	34,683,000	39,825,000
Depreciation and amortization									10,208,000	12,397,000	7,751,000
Stock-based compensation									1,192,000	2,391,000	2,475,000
Capital expenditures									5,933,000	4,415,000	5,127,000
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Segment operating income (loss)									(45,768,000)	(55,157,000)	(40,856,000)
Depreciation and amortization									868,000	762,000	1,098,000
Stock-based compensation									1,880,000	4,659,000	2,134,000
Capital expenditures									$ 36,000	$ 67,000	$ 23,000

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Fixed assets, net book value	$ 81,054				$ 88,189				$ 81,054	$ 88,189
Intangible Assets, Net (Including Goodwill)	795,567				808,720				795,567	808,720
Services	381,975	$ 342,907	$ 362,130	$ 328,791	393,662	$ 375,830	$ 379,743	$ 326,968	1,415,803	1,476,203	$ 1,513,779
UNITED STATES
Segment Reporting Information [Line Items]
Fixed assets, net book value	68,497				76,781				68,497	76,781
Intangible Assets, Net (Including Goodwill)	668,567				679,344				668,567	679,344
Services									1,116,045	1,153,191	1,172,364
CANADA
Segment Reporting Information [Line Items]
Fixed assets, net book value	4,475				4,779				4,475	4,779
Intangible Assets, Net (Including Goodwill)	64,842				61,748				64,842	61,748
Services									105,067	124,001	123,093
Other
Segment Reporting Information [Line Items]
Fixed assets, net book value	8,082				6,629				8,082	6,629
Intangible Assets, Net (Including Goodwill)	$ 62,158				$ 67,628				62,158	67,628
Services									$ 194,691	$ 199,011	$ 218,322

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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 381,975	$ 342,907	$ 362,130	$ 328,791	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 1,415,803	$ 1,476,203	$ 1,513,779
Cost of services sold	260,725	222,448	240,749	237,154	256,088	238,690	253,390	243,030	961,076	991,198	1,023,476
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(1,696)	5,513	7,333	316	(75,713)	(13,667)	5,951	(28,519)			257,223
Net loss attributable to MDC Partners Inc.	$ (7,115)	$ (1,752)	$ 4,290	$ (113)	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ (4,690)	$ (123,733)	$ 241,848
Earnings Per Share, Basic	$ (0.15)	$ (0.07)	$ 0.01	$ (0.04)	$ (1.46)	$ (0.32)	$ 0.02	$ (0.56)
Earnings Per Share, Diluted	$ (0.15)	$ (0.07)	$ 0.01	$ (0.04)	$ (1.46)	$ (0.32)	$ 0.02	$ (0.56)

Quarterly Results of Operatio_4

Quarterly Results of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition, Contingent Consideration [Line Items]
Foreign exchange gain (loss)	$ 4,349	$ (13,324)	$ 8,750	$ (23,258)	$ 18,137
Stock-based compensation	18,408	1,534	31,040	18,416	24,350
Goodwill and other asset impairment	5,875	56,732	7,819	80,057	$ 4,415
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	(2,830)	49,447
Contingent Payment
Business Acquisition, Contingent Consideration [Line Items]
(Income) loss attributable to fair value adjustments	$ 9,030	$ (8,979)	$ 5,403	$ (3,679)