Stagwell (STGW) 10-K 18 Mar 19 2018 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Feb. 28, 2019	Jun. 29, 2018
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
Document Type	10-K
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 0
Common Class A
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		58,432,677
Common Class B
Document Information [Line Items]
Entity Common Stock, Shares Outstanding		3,755

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Services	$ 1,476,203,000	$ 1,513,779,000	$ 1,385,785,000
Operating Expenses:
Cost of services sold	991,198,000	1,023,476,000	936,133,000
Office and general expenses	349,056,000	310,455,000	306,251,000
Depreciation and amortization	46,196,000	43,474,000	46,446,000
Asset Impairment Charges	80,057,000	4,415,000	48,524,000
Costs and Expenses, Total	1,466,507,000	1,381,820,000	1,337,354,000
Operating income	9,696,000	131,959,000	48,431,000
Interest Expense, Other	(67,075,000)	(64,364,000)	(65,050,000)
Other Income (Expenses):
Interest expense and finance charges, net	230,000	1,346,000	414,000
Foreign exchange gain (loss)	23,258,000	(18,137,000)	213,000
Loss on redemption of Notes	0	0	(33,298,000)
Nonoperating Income (Expense), Total	(90,103,000)	(44,881,000)	(98,147,000)
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates	(80,407,000)	87,078,000	(49,716,000)
Income tax expense (benefit)	31,603,000	(168,064,000)	(9,404,000)
Income (loss) before equity in earnings of non-consolidated affiliates	(112,010,000)	255,142,000	(40,312,000)
Equity in earnings (losses) of non-consolidated affiliates	62,000	2,081,000	(309,000)
Income (loss) from continuing operations	(111,948,000)	257,223,000	(40,621,000)
Net income (loss)	(111,948,000)	257,223,000	(40,621,000)
Net income attributable to the noncontrolling interests	(11,785,000)	(15,375,000)	(5,218,000)
Net income (loss) attributable to MDC Partners Inc.	(123,733,000)	241,848,000	(45,839,000)
Accretion on Convertible Preferred Shares	(8,355,000)	6,352,000	0
Net Income (Loss) Available to Common Stockholders, Basic	$ (132,088,000)	$ 205,594,000	$ (45,839,000)
Income (Loss) from Continuing Operations, Per Basic Share	$ (2.31)	$ 3.72	$ (0.89)
Basic
Earnings Per Share, Basic	(2.31)	3.72	(0.89)
Income (Loss) from Continuing Operations, Per Diluted Share	(2.31)	3.71	(0.89)
Earnings Per Share, Diluted	$ (2.31)	$ 3.71	$ (0.89)
Weighted Average Number of Shares Outstanding, Basic	57,218,994	55,255,797	51,345,807
Stock-based compensation expense is included in the following line items above:
Cost of services sold	$ 18,416,000	$ 24,350,000	$ 21,003,000
Share-based Compensation	$ 18,416,000	$ 24,350,000	$ 21,003,000
Weighted Average Number of Shares Outstanding, Diluted	57,218,994	55,481,786	51,345,807
Cost of Sales [Member]
Stock-based compensation expense is included in the following line items above:
Cost of services sold	$ 12,513,000	$ 19,015,000	$ 14,237,000
Share-based Compensation	12,513,000	19,015,000	14,237,000
General and Administrative Expense [Member]
Stock-based compensation expense is included in the following line items above:
Cost of services sold	5,903,000	5,335,000	6,766,000
Share-based Compensation	5,903,000	5,335,000	$ 6,766,000
Convertible preference shares | Convertible Preference Shares
Other Income (Expenses):
Accretion on Convertible Preferred Shares	$ (8,355,000)	$ (36,254,000)

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Comprehensive Income (Loss)
Net income (loss)	$ (111,948)	$ 257,223	$ (40,621)
Other comprehensive income (loss), net of applicable tax:
Foreign currency translation adjustment	3,158	3,611	(4,586)
Benefit plan adjustment, net of income tax expense of $223 in 2018 and nil for 2017 and 2016	555	(1,336)	(3,101)
Other comprehensive income (loss)	3,713	2,275	(7,687)
Comprehensive income (loss) for the year	(108,235)	259,498	(48,308)
Comprehensive income attributable to the noncontrolling interests	(8,824)	(17,780)	(5,612)
Comprehensive income (loss) attributable to MDC Partners Inc.	$ (117,059)	$ 241,718	$ (53,920)

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Benefit plan adjustment income tax expense	$ (223,000)	$ 0	$ 0

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current Assets:
Cash and cash equivalents	$ 30,873	$ 46,179
Cash held in trusts	0	4,632
Accounts receivable, less allowance for doubtful accounts of $1,879 and $2,453	395,200	434,072
Assets held for sale	78,913	0
Expenditures billable to clients	42,369	31,146
Other current assets	42,499	26,742
Total Current Assets	589,854	542,771
Fixed assets, at cost, less accumulated depreciation of $128,546 and $123,599	88,189	90,306
Investment in non-consolidated affiliates	6,556	6,307
Goodwill	740,955	835,935
Other intangible assets, net, less accumulated amortization of $161,868 and $173,546	67,765	70,605
Deferred tax assets	92,741	115,325
Other assets	25,513	37,643
Total Assets	1,611,573	1,698,892
Current Liabilities:
Accounts payable	221,995	244,527
Trust liability	0	4,632
Accruals and other liabilities	312,785	327,812
Liabilities held for sale	35,967	0
Advance billings	138,505	148,133
Current portion of long-term debt	356	313
Current portion of deferred acquisition consideration	32,928	50,213
Total Current Liabilities	742,536	775,630
Long-term debt, less current portion	954,229	882,806
Long-term portion of deferred acquisition consideration	50,767	72,213
Other liabilities	54,133	54,110
Deferred tax liabilities	5,329	6,760
Total Liabilities	1,806,994	1,791,519
Redeemable Noncontrolling Interests	51,546	62,886
Commitments, Contingencies and Guarantees (See Note 18)
Shareholders’ Deficit:
Convertible preference shares, 95,000 authorized, issued and outstanding at December 31, 2018 and 2017	90,123	90,220
Common stock and other paid in capital	58,579	38,191
Accumulated deficit	(464,903)	(340,000)
Accumulated other comprehensive loss	4,720	(1,954)
MDC Partners Inc. Shareholders’ Deficit	(311,481)	(213,543)
Noncontrolling Interests	64,514	58,030
Total Shareholders’ Deficit	(246,967)	(155,513)
Total Liabilities, Redeemable Noncontrolling Interests and Shareholders’ Deficit	$ 1,611,573	$ 1,698,892

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 1,879	$ 2,453
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	128,546	123,599
Finite-Lived Intangible Assets, Accumulated Amortization	$ 80,934	$ 86,773
Preferred Stock, Shares Authorized	95,000	95,000
Preferred stock, shares issued	95,000	95,000
Preferred Stock, Shares Outstanding	95,000	95,000
Other Intangible Assets
Finite-Lived Intangible Assets, Accumulated Amortization	$ 161,868	$ 173,546

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows provided by (used in) operating activities:
Net income (loss)					$ (111,948,000)	$ 257,223,000	$ (40,621,000)
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	$ (75,713,000)	$ (28,519,000)	$ 231,455,000	$ (9,683,000)	(111,948,000)	257,223,000	(40,621,000)
Share-based Compensation	1,534,000		7,480,000		18,416,000	24,350,000	21,003,000
Adjustments to reconcile income to cash provided by (used in) operating activities:
Depreciation					27,111,000	23,873,000	22,293,000
Amortization of intangibles					19,085,000	19,601,000	24,153,000
Amortization of deferred finance charges and debt discount					3,193,000	3,022,000	9,135,000
Asset Impairment Charges	56,732,000				80,057,000	4,415,000	48,524,000
Loss on redemption of Notes					0	0	26,873,000
Adjustment to deferred acquisition consideration					(374,000)	(4,819,000)	8,227,000
Deferred income taxes					23,573,000	(173,019,000)	(10,038,000)
(Earnings) losses of non-consolidated affiliates					(62,000)	(2,081,000)	309,000
Distributions from non-consolidated affiliates					963,000	3,672,000	7,402,000
Other and non-current assets and liabilities					392,000	(4,420,000)	13,527,000
Foreign exchange					20,795,000	(17,637,000)	(8,240,000)
Changes in working capital:
Accounts receivable					30,211,000	(50,030,000)	(16,752,000)
Expenditures billable to clients					11,223,000	(1,892,000)	(13,048,000)
Prepaid expenses and other current assets					(17,189,000)	6,569,000	(13,608,000)
Accounts payable, accruals and other current liabilities					(18,222,000)	13,398,000	(110,018,000)
Acquisition related payments					(29,141,000)	(42,790,000)	(44,914,000)
Cash in trust					(656,000)	(709,000)	219,000
Advance billings					(14,871,000)	14,548,000	11,397,000
Net cash provided by (used in) operating activities					17,280,000	71,786,000	(45,907,000)
Gain (Loss) on Disposition of Assets					(1,867,000)	(1,600,000)	(424,000)
Cash flows used in investing activities:
Capital expenditures					(20,264,000)	(32,958,000)	(29,432,000)
Increase (Decrease) in Deposit Assets					0	0	2,528,000
Payments for (Proceeds from) Investments					2,082,000	10,631,000	666,000
Acquisitions, net of cash acquired					(32,713,000)	0	2,531,000
Other investments					(499,000)	(2,229,000)	(3,835,000)
Net cash used in investing activities					(50,431,000)	(20,884,000)	(25,196,000)
Cash flows provided by (used in) financing activities:
Acquisition related payments					(32,172,000)	(57,083,000)	(90,779,000)
Distributions to noncontrolling interests					(13,419,000)	(8,865,000)	(7,772,000)
Proceeds from exercise of options						0	0
Payment of dividends					(196,000)	(284,000)	(32,918,000)
Repayment of long-term debt					(146,000)	(404,000)	(507,000)
Premium paid on redemption of Notes					0	0	(26,873,000)
Deferred financing costs					0	0	(21,569,000)
Purchase of shares					(776,000)	(1,758,000)	(3,350,000)
Net cash provided by (used in) financing activities					21,434,000	(32,599,000)	35,657,000
Effect of exchange rate changes on cash, cash equivalents, and cash held in trusts					77,000	(754,000)	2,128,000
Net increase (decrease) in cash, cash equivalents, and cash held in trusts including cash classified within assets held for sale					(11,640,000)	17,549,000	(33,318,000)
Net increase (decrease) in cash, cash equivalents, and cash held in trusts					(19,938,000)	17,549,000	(33,318,000)
Cash, cash equivalents, and cash held in trusts at beginning of year		$ 50,811,000		$ 33,262,000	50,811,000	33,262,000	66,580,000
Cash, cash equivalents, and cash held in trusts at end of year	30,873,000		50,811,000		30,873,000	50,811,000	33,262,000	$ 66,580,000
Supplemental disclosures:
Cash income taxes paid					3,836,000	8,099,000	2,895,000
Cash interest paid					64,012,000	62,895,000	64,671,000
Non-cash transactions:
Capital leases					95,000	670,000	265,000
Notes Receivable in exchange for shares of subsidiary						0	6,139,000	0
Dividends Payable	$ 196,000		$ 453,000		196,000	453,000	739,000
Stock Issued During Period, Value, Acquisitions							34,219,000
Leasehold improvements financed by landlord						0	0	$ 7,250,000
Six Point Five Zero Percentage Notes [Domain]
Cash flows provided by (used in) financing activities:
Proceeds from issuance of notes					0	0	900,000,000
6.75% Notes
Cash flows provided by (used in) financing activities:
Repayment of 6.75% Notes					0	0	(735,000,000)
Wells Fargo Capital Finance, Llc [Member] | Revolving Credit Facility [Member]
Cash flows provided by (used in) financing activities:
Repayments of Lines of Credit					(1,625,862,000)	(1,479,632,000)	(1,790,108,000)
Proceeds from Lines of Credit					1,694,005,000	1,425,207,000	1,844,533,000
Net decrease in cash, cash equivalents, and cash held in trusts classified within assets held for sale					(8,298,000)	0	0
Convertible preference shares
Cash flows provided by (used in) financing activities:
Proceeds from Issuance of Convertible Preferred Stock					0	95,000,000	0
Convertible Preferred Stock [Member]
Cash flows provided by (used in) financing activities:
Payments of Stock Issuance Costs					0	(4,780,000)	0
Common Class A
Non-cash transactions:
Redemption value adjustments						3,353,939
Common Stock
Non-cash transactions:
Redemption value adjustments					0
Common Stock | Common Class A
Non-cash transactions:
Redemption value adjustments						28,727,000	10,458,000
Forsman & Bodenfors AB [Domain] | Common Stock | Common Class A
Non-cash transactions:
Stock Issued During Period, Value, Acquisitions					$ 7,030,000	$ 0	$ 34,219,000

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical)	Dec. 31, 2014	Dec. 31, 2013	Mar. 20, 2013
6.75% Notes
Stated interest rate	6.75%	6.75%	6.75%

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Convertible Preference SharesSeries 4 Convertible Preferred Stock [Member]	Common Stock	Share Capital to Be Issued	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss	MDC Partners Inc. Shareholders’ Deficit	Noncontrolling Interests	Contingent Consideration, Liability Settlements [Domain]	Contingent Consideration, Liability Settlements [Domain]Convertible Preference SharesSeries 4 Convertible Preferred Stock [Member]	Contingent Consideration, Liability Settlements [Domain]Common Stock	Contingent Consideration, Liability Settlements [Domain]MDC Partners Inc. Shareholders’ Deficit	Aggregate 2017 Dispositions [Domain]	Aggregate 2017 Dispositions [Domain]Noncontrolling Interests
Stockholders' equity, beginning balance at Dec. 31, 2015	$ (496,092)			$ 0	$ (45,419)	$ (536,009)	$ 6,257	$ (575,171)	$ 79,079
Common stock outstanding, beginning balance (in shares) at Dec. 31, 2015			49,990,460	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Value, Restricted Stock Award, Net of Forfeitures	$ 12,818				10,458			12,818
Stock Issued During Period, Shares, New Issues	0		691,559
Net income attributable to MDC Partners	$ (45,839)					(45,839)		(45,839)
Other comprehensive income (loss)	(7,687)						(8,081)	(8,081)	394
Stock Appreciation Rights Exercised (in shares)				(100,000)
Stock Authorized During Period, Value, To be Issued				$ (2,360)
Issuance of restricted stock (in shares)			425,915
Stock Issued During Period, Value, Acquisitions	34,219				34,219			34,219
Deferred acquisition consideration settled through issuance of shares	(3,350)				(3,350)			(3,350)
Options Exercised	9,604
Shares issued, acquisitions	10,662				10,662			10,662
Increase (decrease) in noncontrolling interests and redeemable noncontrolling interests from business acquisitions and step-up transactions	(32,747)				(32,747)			(32,747)
Common stock outstanding, ending balance (in shares) at Dec. 31, 2016			52,802,058	100,000
Stockholders' equity, ending balance at Dec. 31, 2016	(509,476)			$ 2,360	6,203	(581,848)	(1,824)	(575,109)	65,633
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	8,936				22,776			22,776	(13,840)
Stock Issued During Period, Shares, New Issues			(205,876)
Stock Issued During Period, Shares, Acquisitions			(1,900,000)
Temporary Equity, Accretion to Redemption Value					(9,604)			(9,604)
Stock Issued During Period, Shares, New Issues											95,000,000
Net income attributable to MDC Partners	241,848					241,848		241,848
Other comprehensive income (loss)	2,275						(130)	(130)	2,405
Stock Appreciation Rights Exercised (in shares)				100,000
Stock Authorized During Period, Value, To be Issued	(27,852)			$ 2,360	(30,212)			(27,852)
Issuance of restricted stock (in shares)			380,669
Deferred acquisition consideration settled through issuance of shares	(1,758)				(1,758)			(1,758)
Shares issued, acquisitions					8,028			8,028
Increase (decrease) in noncontrolling interests and redeemable noncontrolling interests from business acquisitions and step-up transactions	(9,650)
Noncontrolling Interest, Increase from Business Combination	1,666				(5,654)			(5,654)	12,614
Changes in noncontrolling interest and redeemable noncontrolling interests from business dispositions	6,960
Common stock outstanding, ending balance (in shares) at Dec. 31, 2017			56,375,131
Stockholders' equity, ending balance at Dec. 31, 2017	(155,513)	$ 90,220			38,191	(340,000)	(1,954)	(213,543)	58,030
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					2,315			2,315	(11,965)
Increase (Decrease) in Redemption Value of Redeemable Noncontrolling Interests	(1,498)
Stock Issued During Period, Shares, New Issues			3,353,939
Redemption value adjustments										$ 90,220	$ 90,220		$ 90,220
Stock Issued During Period, Shares, Acquisitions			161,535
Temporary Equity, Accretion to Redemption Value	(8,028)				1,498			1,498
Adjustments to Additional Paid in Capital, Other	343				343			343
Noncontrolling Interest, Decrease from Deconsolidation														$ (10,657)	$ (10,657)
Shares, Outstanding		95,000,000
Net income attributable to MDC Partners	(123,733)					(123,733)		(123,733)
Other comprehensive income (loss)	3,713						6,674	6,674	(2,961)
Issuance of restricted stock (in shares)												1,011,561
Stock Issued During Period, Value, Acquisitions					7,030					$ 7,030			$ 7,030
Deferred acquisition consideration settled through issuance of shares	(776)				(776)			(776)
Shares issued, acquisitions	8,165				8,165			8,165
Noncontrolling Interest, Change in Redemption Value	(5,965)								(5,965)
Noncontrolling Interest, Increase from Business Combination	0
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification	(1,170)					(1,170)		(1,170)
Common stock outstanding, ending balance (in shares) at Dec. 31, 2018			57,521,323
Stockholders' equity, ending balance at Dec. 31, 2018	(246,967)	$ 90,123			58,579	$ (464,903)	$ 4,720	(311,481)	64,514
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Issued During Period, Shares, Restricted Stock Award, Net of Forfeitures			243,529
Stock Issued During Period, Value, Convertible Preferred Shares	(97)	$ (97)						(97)
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	25,550				10,140			10,140	$ 15,410
Increase (Decrease) in Redemption Value of Redeemable Noncontrolling Interests	$ (4,171)
Redemption value adjustments			$ 0
Stock Issued During Period, Shares, Acquisitions			(108,898)
Temporary Equity, Accretion to Redemption Value					$ 4,171			$ 4,171
Shares, Outstanding		95,000,000

Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	1. 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. 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 generally accepted accounting principles of the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for reporting financial information on Form 10-K. 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 primarily in the U.S., Canada, Europe, Asia, and Latin America. Recent Developments Strategic Review Process and Successor CEO Search On September 20, 2018, the Company announced its evaluation of potential strategic alternatives, which included, among other things, the possible sale of the Company. On September 12, 2018, the Company announced that Scott Kauffman’s employment as the Company’s Chief Executive Officer would terminate, which it did effective December 31, 2018. The strategic review process proceeded in parallel with the Company’s search to identify a successor CEO. During the interim period in which the Company was evaluating strategic alternatives and assessing potential new CEO candidates, the Board of Directors has established an executive committee comprised of David Doft (EVP, Chief Financial Officer), Mitchell Gendel (EVP, General Counsel), Stephanie Nerlich (EVP, Partner Development and Talent), and David Ross (EVP, Strategy & Corporate Development) (collectively, the “Executive Committee”). Effective January 1, 2019, the Executive Committee assumed the role and responsibilities of the Chief Executive Officer until the appointment of a successor. The Board of Directors’ Strategic Alternatives Committee, comprised of three independent directors of the Board (Irwin Simon, Larry Kramer and Anne Marie O’Donovan), have provided oversight for the Executive Committee during the interim period. The Company has completed the strategic review process and search for a new CEO. On March 14, 2019, the Company entered into a securities purchase agreement with Stagwell Agency Holdings LLC (“Stagwell Holdings”), an affiliate of Stagwell Group LLC (“Stagwell”), pursuant to which Stagwell Holdings agreed to purchase, (i) 14,285,714 newly authorized Class A shares for $3.50 per share for an aggregate purchase price of $50 million and (ii) 50,000 newly authorized Series 6 convertible preference shares for an aggregate purchase price of $50 million . See Note 23 of the Notes to the Consolidated Financial Statements included herein for additional information. Effective March 18, 2019, the Company’s Board of the Directors appointed Mark Penn as the Chief Executive Officer (succeeding the Executive Committee) and as a director of the Board. Mr. Penn is manager of Stagwell. Amendment to Credit Agreement On March 12, 2019 , the Company, Maxxcom Inc. (a subsidiary of the Company) (“Maxxcom”) and each of their subsidiaries party thereto entered into an amendment (the “Amendment”) to the existing senior secured revolving credit facility, dated as of May 3, 2016 (as amended, the “Credit Agreement”), among the Company, Maxxcom Inc., a Delaware corporation, each of their subsidiaries party thereto, Wells Fargo Capital Finance, LLC, as agent (“Wells Fargo”), and the lenders from time to time party thereto. See Note 12 of the Notes to the Consolidated Financial Statements included herein for additional information regarding the amendments to the Credit Agreement. Sale of Kingsdale On March 8, 2019, the Company consummated the sale of its Kingsdale business, including operations in Toronto and New York City, back to the Kingsdale Founder and CEO. As consideration for the sale, the Company was paid cash plus the assumption of certain liabilities totaling approximately $50 million in the aggregate.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
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. Reclassifications. Certain reclassifications have been made to the prior period consolidated financial statements to conform to the current period presentation. Additionally, certain changes to presentation have been made. The Company changed its presentation of net income allocated to convertible preference shareholders. In the Company’s Form 10-K for the year ended December 31, 2017, this amount was presented in the Income (Loss) per Common Share footnote and not on the Consolidated Statements of Operations. In connection with the presentation of the Form 10-K for the year ended December 31, 2018, the Company changed the 2017 Consolidated Statement of Operations to include the net income allocated to convertible preference shares, which was previously disclosed in footnote 3 of the December 31, 2017 financial statements. Use of Estimates . The preparation of consolidated financial statements in conformity with U.S. 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 15 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, 2018 and 2017 . No sales to an individual client or country other than the United States accounted for more than 10% of revenue for the fiscal years ended December 31, 2018, 2017, or 2016. 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, and 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. Cash in Trust. A subsidiary of the Company holds restricted cash in trust accounts related to funds received on behalf of clients. Such amounts are held in escrow under depositary service agreements and distributed at the direction of the clients. The funds are presented as a corresponding liability on the balance sheet. As of December 31, 2018, cash held in trusts and the trust liability totaling $3,976 were classified within assets and liabilities held for sale within the Consolidated Balance Sheet. Refer to Note 5 in the Notes to Consolidated Financial Statements included herein for further information regarding the sale of this subsidiary. 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. 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. 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, 2018 and 2017 was $8,072 and $9,527 , 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 effective January 1, 2018. 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 tradename) 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 2018 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 and demand trends and appropriate discount rates based on a reporting units 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. We performed the quantitative impairment test in 2018. See Note 10 for additional information regarding the Company’s impairment test and impairment charges recognized. 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 10 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 trade names. In executing the Company’s overall acquisition strategy, one of the primary drivers in identifying and executing a specific transaction is the existence of, or the ability to, expand the existing client relationships. The expected benefits of the Company’s acquisitions are typically shared across multiple agencies and regions. Deferred Acquisition Consideration . Consistent with our acquisition strategy and 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 is recorded as a deferred acquisition consideration liability and are derived from the 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 and 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 of the Company, the amounts are recorded as redeemable noncontrolling interests in mezzanine equity on the balance sheet at their acquisition date fair value and adjusted for changes to their estimated redemption value through additional paid-in capital (but not less than their initial redemption value), except for foreign currency translation adjustments. These adjustments will not impact the calculation of earnings (loss) per share if the redemption values are less than the estimated fair values. There was no impact on the Company’s earnings (loss) per share calculation in any period. 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 additional paid-in capital. 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 . Effective January 1, 2018, the Company adopted Financial Accounting Standards Board (the “FASB”) ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). 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 3 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. See Note 11 of the Notes to the Consolidated Financial Statements included herein for information related to the 2017 Tax Cuts and Jobs Act (the “Tax Act”) enacted into law on December 22, 2017, and Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”) issued by the SEC in December 2017. 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 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 U.S. and Canadian 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 $9,810 , $10,124 and $10,026 for the years ended December 31, 2018 , 2017 , and 2016 , respectively. The Company also has a defined benefit pension plan. See Note 20 of the Notes to the Consolidated Financial Statements included herein for additional information. 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 95,000 authorized and issued Series 4 Convertible Preference Shares (the “Preference Shares”) sold in a private placement in 2017. 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 14 of the Notes to the Consolidated Financial Statements included herein for additional information. The two-class method is an earnings allocation method under which earnings per share is calculated for common stock considering a participating security’s rights to undistributed earnings as if all such earnings had been distributed during the period. Either the two-class method or the if-converted method is applied to calculate diluted net income per common share, depending on which method results in more dilution. The Company’s participating securities are not included in the computation of net loss per common share in periods of net loss because the convertible preference shareholders have no contractual obligation to participate in losses. Foreign Currency Translation . The functional currency of the Company is the Canadian dollar; however, it has decided to use U.S. dollars as its reporting currency for consolidated reporting purposes. Generally, the Company’s subsidiaries use their local currency as their functional currency. Accordingly, the currency impacts of the translation of the Consolidated Balance Sheets of the Company and its non-U.S. dollar based subsidiaries to U.S. dollar statements are included as cumulative translation adjustments in accumulated other comprehensive income (loss). Translation of intercompany debt, which is not intended to be repaid, is included in cumulative translation adjustments. Cumulative translation adjustments are not included in net earnings 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. The balance sheets of non-U.S. dollar based subsidiaries are translated at the period end rate. The Consolidated Statements of Operating 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 income (loss).

Revenue (Notes)

Revenue (Notes)	12 Months Ended
	Dec. 31, 2018
Revenue [Abstract]
Revenue	Revenue Effective January 1, 2018, the Company adopted ASC Topic 606. ASC 606 was applied using the modified retrospective method, with the cumulative effect of the initial adoption being recognized as an adjustment to opening retained earnings at January 1, 2018. As a result, comparative prior periods have not been adjusted and continue to be reported under FASB ASC Topic 605, Revenue Recognition (“ASC 605”). See Note 19 of the Notes to the Consolidated Financial Statements included herein for additional information surrounding the Company’s adoption of ASC 606. The Company’s revenue recognition policies are established in accordance with the Revenue Recognition topics of 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 nor interdependent, nor that 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, 2018, 2017, and 2016 and the impact of adoption of ASC 606: Twelve Months Ended December 31, 2018 2017 2016 Industry Reportable Segment As reported Adjustment to exclude impact of Adoption of ASC 606 Adjusted Food & Beverage All $ 313,368 $ 7,064 $ 320,432 $ 313,786 $ 266,600 Retail All 152,552 (2,683 ) 149,869 178,152 182,428 Consumer Products All 162,524 585 163,109 162,307 147,849 Communications All 178,410 25,957 204,367 208,701 160,064 Automotive All 88,807 8,587 97,394 127,023 129,352 Technology All 104,479 38 104,517 99,325 109,309 Healthcare All 127,547 507 128,054 124,261 115,159 Financials All 110,069 146 110,215 104,713 85,480 Transportation and Travel/Lodging All 86,419 2,461 88,880 56,955 58,298 Other All 152,028 8,974 161,002 138,556 131,246 $ 1,476,203 $ 51,636 $ 1,527,839 $ 1,513,779 $ 1,385,785 MDC has historically largely focused where the Company was founded in North America, the largest market for its services in the world. In recent years the Company has expanded its global footprint to support clients looking for help to grow their businesses in new markets. Today, MDC’s Partner Firms are located in the United States, Canada, and an additional thirteen 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, 2018, 2017, and 2016 and the impact of adoption of ASC 606: Twelve Months Ended December 31, 2018 2017 2016 Geographic Location Reportable Segment As reported Adjustment to exclude impact of Adoption of ASC 606 Adjusted United States All $ 1,153,192 $ 20,699 $ 1,173,891 $ 1,172,364 $ 1,103,714 Canada All 124,000 (1,288 ) 122,712 123,092 124,101 Other All, Excluding Domestic Creative Agencies 199,011 32,225 231,236 218,323 157,970 $ 1,476,203 $ 51,636 $ 1,527,839 $ 1,513,779 $ 1,385,785 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 $64,362 and $54,177 at December 31, 2018 and December 31, 2017 , 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 $ 42,369 and $31,146 at December 31, 2018 and December 31, 2017 , 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, 2018 and December 31, 2017 were $138,505 and $148,133 , respectively. The decrease in the advance billings balance of $9,628 for the twelve months ended December 31, 2018 is primarily driven by $135,573 of revenues recognized that were included in the advance billings balances as of December 31, 2017 and reductions due to the incurrence of third-party costs, offset by cash payments received or due in advance of satisfying our performance obligations. Changes in the contract asset and liability balances during the twelve months ended December 31, 2018 and December 31, 2017 were not materially impacted by write offs, impairment losses or any other factors. Practical Expedients In adopting 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. Amounts related to those performance obligations with expected durations of more than one year are immaterial.

Loss per Common Share

Loss per Common Share	12 Months Ended
	Dec. 31, 2017
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 for the years ended December 31: 2018 2017 2016 Numerator: Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Accretion on convertible preference shares (8,355 ) (6,352 ) — Net income allocated to convertible preference shares — (29,902 ) — Net income (loss) attributable to MDC Partners Inc. common shareholders (132,088 ) 205,594 (45,839 ) Adjustment to net income allocated to convertible preference shares — 106 — Net income (loss) attributable to MDC Partners Inc. common shareholders $ (132,088 ) $ 205,700 $ (45,839 ) Denominator: Basic weighted average number of common shares outstanding 57,218,994 55,255,797 51,345,807 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 57,218,994 55,481,786 51,345,807 Net income (loss) attributable to MDC Partners Inc. common shareholders per common share: Basic $ (2.31 ) $ 3.72 $ (0.89 ) Diluted $ (2.31 ) $ 3.71 $ (0.89 ) Anti-dilutive stock awards 1,442,518 - 1,391,456 Restricted stock and restricted stock unit awards of 1,012,637 , 1,443,921 , and 503,321 for the twelve months ended December 31, 2018, 2017, and 2016, respectively, which are contingent upon the Company meeting a cumulative three year earnings target (2018, 2019, and 2020) 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, 2018, 2017, and 2016, respectively. In addition, there were 95,000 shares of Preference Shares outstanding which were convertible into 10,970,714 and 10,135,244 Class A common shares at December 31, 2018 and 2017, respectively. These Preference Shares were anti-dilutive for the twelve months ended December 31, 2018 and 2017 and are therefore excluded from the diluted income (loss) per common share calculation.

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Acquisitions	. Acquisitions and Dispositions 2018 Acquisitions On September 7, 2018, a subsidiary of the Company purchased 100% interests of OneChocolate Communications Limited and OneChocolate Communications LLC, PR (“OneChocolate”) a digital marketing consultancy headquartered in London, UK, for an aggregate purchase price of $3,231 , working capital payment of $966 and additional deferred acquisition payments with an estimated present value of $2,146 . OneChocolate’s results are reflected in the Allison & Partners operating segment which is included in the Specialist Communications reportable segment which had an immaterial impact on our results. On July 1, 2018, the Company acquired the remaining 14.87% and 3% of membership interests of Doner Partners, LLC and Source Marketing LLC respectively for an aggregate purchase price of $7,618 , comprised of a closing cash payment of $3,279 and additional deferred acquisition payments with an estimated present value of $4,305 as of December 31, 2018. As of the acquisition date, the fair value of the additional interests acquired was $16,361 for Doner Partners LLC. The fair values were measured using a discounted cash flow model. As a result of the transaction, the Company reduced noncontrolling interest by $11,946 and redeemable noncontrolling interest by $933 . On April 2, 2018, the Company purchased 51% of the membership interests of Instrument LLC (“Instrument”), a digital creative agency based in Portland, Oregon, for an aggregate purchase price of $35,591 . The acquisition is expected to facilitate the Company’s growth and help to build its portfolio of modern, innovative and digital-first agencies. The purchase price consisted of a cash payment of $28,561 and the issuance of 1,011,561 shares of the Company’s Class A subordinate voting stock with an acquisition date fair value of $7,030 . The Company issued these shares in a transaction exempt from the registration requirements of the Securities Act of 1933, as amended, pursuant to Section 4(a)(2) of the Securities Act. The purchase price allocation for Instrument resulted in tangible assets of $10,304 , identifiable intangibles of $23,130 , consisting primarily of customer lists and a trade name, and goodwill of $32,776 . In addition, the Company has recorded $27,357 as the fair value of noncontrolling interests, which was derived from the Company’s purchase price less a discount related to the noncontrolling parties’ lack of control. The identified assets have a weighted average useful life of approximately six years and will be amortized in a manner represented by the pattern in which the economic benefits of such assets are expected to be realized. The goodwill is tax deductible. Instruments’ results are included in the All Other category from a segment reporting perspective. The Company has a controlling financial interest in Instrument through its majority voting interest, and as such, has aggregated the acquired Partner Firm’s financial data into the Company’s consolidated financial statements. The operating results of Instrument in the current year is not material. Effective January 1, 2018, the Company acquired the remaining 24.5% ownership interest of Allison & Partners LLC for an aggregate purchase price of $10,023 , comprised of a closing cash payment of $300 and additional deferred acquisition payments with an estimated present value at the acquisition date of $9,723 . The deferred payments are based on the future financial results of the underlying business from 2017 to 2020 with final payments due in 2021. As of the acquisition date, the fair value of the additional interest acquired was $20,096 . The fair value was measured using a discounted cash flow model. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $8,857 . The difference between the purchase price and the noncontrolling interest of $1,166 was recorded in additional paid-in capital. Assets and Liabilities Held for Sale The Company has initiated a process to sell its ownership interest in Kingsdale, an operating segment that provides shareholder services, and a foreign office within the Global Integrated Agencies reportable segment. The assets and liabilities of both entities 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. The significant assets classified as held for sale were accounts receivable and goodwill and significant liabilities were accounts payable and accrued liabilities. This also resulted in a write down of goodwill of Kingsdale totaling $4,691 . This charge is included in Goodwill and other asset impairment within the Consolidated Statement of Operations for the year ended December 31, 2018. The sale of Kingsdale was consummated on March 8, 2019. See Note 1 of the Notes to the Consolidated Financial Statements for additional information. The sale of the foreign office is expected to be completed within the next twelve months. 2017 Acquisitions In 2017, the Company entered into various non-material transactions in connection with certain of its majority-owned entities. As a result of the foregoing, the Company made total cash closing payments of $3,858 , increased fixed deferred consideration liability by $7,208 , reduced redeemable noncontrolling interests by $816 , reduced noncontrolling interests equity by $11,965 , reduced noncontrolling interest payable by $397 , and increased additional paid-in capital by $2,315 . In addition, a stock-based compensation charge of $996 has been recognized representing the consideration paid in excess of the fair value of the interest acquired. 2017 Dispositions During 2017, the Company sold all of its ownership interests in three subsidiaries resulting in recognition of a net loss on sale of business of $1,732 . The net assets reflected in the calculation of the net loss on sale was inclusive of goodwill of $17,593 . Goodwill was allocated to the subsidiaries based on the relative fair value of the sold subsidiaries compared to the fair value of the respective reporting units. Additionally, the Company recorded a reduction in noncontrolling interests of $10,657 . In addition, the Company sold a noncontrolling ownership interest in two subsidiaries during 2017. The Company recorded $6,961 of noncontrolling interest equity and $1,690 of redeemable noncontrolling interest, representing the fair value of the disposed ownership interest at the time of execution. Additionally, stock-based compensation of $2,473 was recognized, representing the excess in the proportionate fair value over the total consideration received. Deferred Acquisition Considerations 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 are 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, 2018 and 2017. 2018 2017 Beginning balance of contingent payments $ 119,086 $ 224,754 Payments (1) (54,947 ) (110,234 ) Additions - acquisition and step-up transactions 14,943 — Redemption value adjustments (2) 3,512 3,273 Foreign translation adjustment 4 1,293 Ending balance of contingent payments $ 82,598 $ 119,086 Fixed payments (3) 1,097 3,340 $ 83,695 $ 122,426 (1) For the twelve months ended December 31, 2017 , payments include $28,727 of deferred acquisition consideration settled through the issuance of 3,353,939 MDC Class A subordinate voting shares in lieu of cash. (2) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments, including the accretion of present value 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. (3) The Company made $6,366 in fixed payments for the twelve months ended December 31, 2018 . The following table presents the impact to the Company’s statement of operations due to redemption value adjustments for the twelve months ended December 31, 2018 and 2017: 2018 2017 Income attributable to fair value adjustments $ (3,679 ) $ (6,021 ) Stock-based compensation expense 7,191 9,294 Redemption value adjustments $ 3,512 $ 3,273

Deferred Acquisition Considerat

Deferred Acquisition Considerations (Notes)	12 Months Ended
	Dec. 31, 2018
Business Combinations [Abstract]
Deferred Acquisition Considerations	. Acquisitions and Dispositions 2018 Acquisitions On September 7, 2018, a subsidiary of the Company purchased 100% interests of OneChocolate Communications Limited and OneChocolate Communications LLC, PR (“OneChocolate”) a digital marketing consultancy headquartered in London, UK, for an aggregate purchase price of $3,231 , working capital payment of $966 and additional deferred acquisition payments with an estimated present value of $2,146 . OneChocolate’s results are reflected in the Allison & Partners operating segment which is included in the Specialist Communications reportable segment which had an immaterial impact on our results. On July 1, 2018, the Company acquired the remaining 14.87% and 3% of membership interests of Doner Partners, LLC and Source Marketing LLC respectively for an aggregate purchase price of $7,618 , comprised of a closing cash payment of $3,279 and additional deferred acquisition payments with an estimated present value of $4,305 as of December 31, 2018. As of the acquisition date, the fair value of the additional interests acquired was $16,361 for Doner Partners LLC. The fair values were measured using a discounted cash flow model. As a result of the transaction, the Company reduced noncontrolling interest by $11,946 and redeemable noncontrolling interest by $933 . On April 2, 2018, the Company purchased 51% of the membership interests of Instrument LLC (“Instrument”), a digital creative agency based in Portland, Oregon, for an aggregate purchase price of $35,591 . The acquisition is expected to facilitate the Company’s growth and help to build its portfolio of modern, innovative and digital-first agencies. The purchase price consisted of a cash payment of $28,561 and the issuance of 1,011,561 shares of the Company’s Class A subordinate voting stock with an acquisition date fair value of $7,030 . The Company issued these shares in a transaction exempt from the registration requirements of the Securities Act of 1933, as amended, pursuant to Section 4(a)(2) of the Securities Act. The purchase price allocation for Instrument resulted in tangible assets of $10,304 , identifiable intangibles of $23,130 , consisting primarily of customer lists and a trade name, and goodwill of $32,776 . In addition, the Company has recorded $27,357 as the fair value of noncontrolling interests, which was derived from the Company’s purchase price less a discount related to the noncontrolling parties’ lack of control. The identified assets have a weighted average useful life of approximately six years and will be amortized in a manner represented by the pattern in which the economic benefits of such assets are expected to be realized. The goodwill is tax deductible. Instruments’ results are included in the All Other category from a segment reporting perspective. The Company has a controlling financial interest in Instrument through its majority voting interest, and as such, has aggregated the acquired Partner Firm’s financial data into the Company’s consolidated financial statements. The operating results of Instrument in the current year is not material. Effective January 1, 2018, the Company acquired the remaining 24.5% ownership interest of Allison & Partners LLC for an aggregate purchase price of $10,023 , comprised of a closing cash payment of $300 and additional deferred acquisition payments with an estimated present value at the acquisition date of $9,723 . The deferred payments are based on the future financial results of the underlying business from 2017 to 2020 with final payments due in 2021. As of the acquisition date, the fair value of the additional interest acquired was $20,096 . The fair value was measured using a discounted cash flow model. As a result of the transaction, the Company reduced redeemable noncontrolling interests by $8,857 . The difference between the purchase price and the noncontrolling interest of $1,166 was recorded in additional paid-in capital. Assets and Liabilities Held for Sale The Company has initiated a process to sell its ownership interest in Kingsdale, an operating segment that provides shareholder services, and a foreign office within the Global Integrated Agencies reportable segment. The assets and liabilities of both entities 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. The significant assets classified as held for sale were accounts receivable and goodwill and significant liabilities were accounts payable and accrued liabilities. This also resulted in a write down of goodwill of Kingsdale totaling $4,691 . This charge is included in Goodwill and other asset impairment within the Consolidated Statement of Operations for the year ended December 31, 2018. The sale of Kingsdale was consummated on March 8, 2019. See Note 1 of the Notes to the Consolidated Financial Statements for additional information. The sale of the foreign office is expected to be completed within the next twelve months. 2017 Acquisitions In 2017, the Company entered into various non-material transactions in connection with certain of its majority-owned entities. As a result of the foregoing, the Company made total cash closing payments of $3,858 , increased fixed deferred consideration liability by $7,208 , reduced redeemable noncontrolling interests by $816 , reduced noncontrolling interests equity by $11,965 , reduced noncontrolling interest payable by $397 , and increased additional paid-in capital by $2,315 . In addition, a stock-based compensation charge of $996 has been recognized representing the consideration paid in excess of the fair value of the interest acquired. 2017 Dispositions During 2017, the Company sold all of its ownership interests in three subsidiaries resulting in recognition of a net loss on sale of business of $1,732 . The net assets reflected in the calculation of the net loss on sale was inclusive of goodwill of $17,593 . Goodwill was allocated to the subsidiaries based on the relative fair value of the sold subsidiaries compared to the fair value of the respective reporting units. Additionally, the Company recorded a reduction in noncontrolling interests of $10,657 . In addition, the Company sold a noncontrolling ownership interest in two subsidiaries during 2017. The Company recorded $6,961 of noncontrolling interest equity and $1,690 of redeemable noncontrolling interest, representing the fair value of the disposed ownership interest at the time of execution. Additionally, stock-based compensation of $2,473 was recognized, representing the excess in the proportionate fair value over the total consideration received. Deferred Acquisition Considerations 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 are 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, 2018 and 2017. 2018 2017 Beginning balance of contingent payments $ 119,086 $ 224,754 Payments (1) (54,947 ) (110,234 ) Additions - acquisition and step-up transactions 14,943 — Redemption value adjustments (2) 3,512 3,273 Foreign translation adjustment 4 1,293 Ending balance of contingent payments $ 82,598 $ 119,086 Fixed payments (3) 1,097 3,340 $ 83,695 $ 122,426 (1) For the twelve months ended December 31, 2017 , payments include $28,727 of deferred acquisition consideration settled through the issuance of 3,353,939 MDC Class A subordinate voting shares in lieu of cash. (2) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments, including the accretion of present value 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. (3) The Company made $6,366 in fixed payments for the twelve months ended December 31, 2018 . The following table presents the impact to the Company’s statement of operations due to redemption value adjustments for the twelve months ended December 31, 2018 and 2017: 2018 2017 Income attributable to fair value adjustments $ (3,679 ) $ (6,021 ) Stock-based compensation expense 7,191 9,294 Redemption value adjustments $ 3,512 $ 3,273

Fixed Assets

Fixed Assets	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Fixed Assets	. Fixed Assets The following is a summary of the Company’s fixed assets as of December 31: 2018 2017 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 100,276 $ (73,060 ) $ 27,216 $ 101,806 $ (74,429 ) $ 27,377 Leasehold improvements 116,459 (55,486 ) 60,973 112,099 (49,170 ) 62,929 $ 216,735 $ (128,546 ) $ 88,189 $ 213,905 $ (123,599 ) $ 90,306 At December 31, 2018 and 2017 , included in fixed assets are assets under capital lease obligations with a cost of $1,447 and $1,903 , respectively, and accumulated depreciation of $780 and $1,176 , respectively. Depreciation expense for the years ended December 31, 2018 , 2017 , and 2016 was $27,111 , $23,873 and $22,293 , respectively.

Noncontrolling and Redeemable N

Noncontrolling and Redeemable Noncontrolling Interests (Notes)	12 Months Ended
	Dec. 31, 2018
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 additional paid-in capital (but not less than their initial redemption value), except for foreign currency translation adjustments. On occasion, the Company may initiate a renegotiation to acquire an incremental ownership interest and the amount of consideration paid may differ materially from the amounts recorded in the Company’s 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, 2018 and 2017 were as follows: Noncontrolling Interests Balance, December 31, 2016 $ 4,154 Income attributable to noncontrolling interests 15,375 Distributions made (8,865 ) Other (1) 366 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 (1) Other 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: Year Ended December 31, 2018 2017 2016 Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Transfers from the noncontrolling interests Increase in MDC Partners Inc. paid-in capital for purchase of equity interests in excess of noncontrolling interests and redeemable noncontrolling interests 10,140 2,315 22,776 Net transfers from noncontrolling interests $ 10,140 $ 2,315 $ 22,776 Change from net income (loss) attributable to MDC Partners Inc. and transfers (to) from noncontrolling interests $ (113,593 ) $ 244,163 $ (23,063 ) Redeemable Noncontrolling Interests The following table presents changes in redeemable noncontrolling interests as of December 31, 2018 and 2017 : 2018 2017 Beginning Balance $ 62,886 $ 60,180 Redemptions (11,943 ) (910 ) Granted — 1,666 Changes in redemption value 1,067 1,498 Currency translation adjustments (464 ) 452 Ending balance $ 51,546 $ 62,886 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 $ 51,546 as of December 31, 2018 , consists of $17,373 assuming that the subsidiaries perform over the relevant future periods at their discounted cash flows earnings level and such rights are exercised, $31,567 upon termination of such owner’s employment with the applicable subsidiary or death and $2,606 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. There was no related impact on the Company’s income (loss) per share calculations.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2018
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 15 of the Notes to the Consolidated Financial Statements included herein for additional information for the fair value. The fair value of financial commitments, guarantees and letters of credit, are based on the stated value of the underlying instruments, if any.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	s 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, 2016 $ 350,716 $ 36,762 $ 78,691 $ 176,686 $ 201,904 $ 844,759 Acquired goodwill — — — — — Disposition (964 ) — — (16,629 ) — (17,593 ) Impairment loss recognized (2,741 ) — — (497 ) — (3,238 ) Transfer of goodwill between segments 6,371 — — 497 (6,868 ) — Foreign currency translation 5,689 218 15 — 6,085 12,007 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 (1) See Note 5 of the Notes to the Consolidated Financial Statements included herein for additional information. The Company recognized an impairment of goodwill and other assets of $80,057 for the twelve months ended December 31, 2018 . The impairment primarily consists 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. The impairment of goodwill was in connection with the Company’s interim and annual impairment tests performed in 2018. See below for information regarding an impairment of a tradename. The Company recognized an impairment of goodwill and other assets of $4,415 for the twelve months ended December 31, 2017. The impairment primarily consists 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 impairment of goodwill was in connection with the Company’s annual impairment test performed in 2017. The Company recognized an impairment of goodwill of $48,524 for the twelve months ended December 31, 2016. The impairment was recognized at three reporting units, the Specialist Communications reportable segment, Media Services reportable segment and All Other reportable segment. The impairment of goodwill was in connection with the Company’s interim and annual impairment tests performed in 2016. The total accumulated goodwill impairment charges are $173,205 through December 31, 2018 . As of December 31, the gross and net amounts of acquired intangible assets other than goodwill were as follows: For the Year Ended December 31, Intangible Assets 2018 2017 Trademarks (indefinite life) $ 14,600 $ 17,780 Customer relationships – gross $ 93,296 $ 102,325 Less accumulated amortization (59,144 ) (73,767 ) Customer relationships – net $ 34,152 $ 28,558 Other intangibles – gross $ 40,803 $ 37,273 Less accumulated amortization (21,790 ) (13,006 ) Other intangibles – net $ 19,013 $ 24,267 Total intangible assets $ 148,699 $ 157,378 Less accumulated amortization (80,934 ) (86,773 ) Total intangible assets – net $ 67,765 $ 70,605 In 2018, the Company recognized the full write-down of a trademark totaling $3,180 for a reporting unit within the Global Integrated Agencies reportable segment. The tradename is no longer in active use given its merger with another reporting unit. See Note 16 of the Notes to the Consolidated Financial Statements for information related to the merger. The weighted average amortization period for customer relationships is six years and other intangible assets is eight years . In total, the weighted average amortization period is seven years . Amortization expense related to amortizable intangible assets for the years ended December 31, 2018 , 2017 , and 2016 was $17,290 , $17,125 , and $21,726 , respectively. The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2019 $ 12,257 2020 9,601 2021 8,220 2022 7,666 2023 and thereafter 15,421

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2018
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 U.S. federal corporate tax rate from 35% to 21%, 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 SEC issued SAB 118 which provides guidance on accounting for the tax effects of the Tax Act. SAB 118 provided a measurement period that should not extend beyond one year from the Tax Act enactment date for companies to complete the accounting under ASC 740. The Company has completed its accounting for the provisions of the Act in accordance with SAB 118. As of December 31, 2017 the Company recorded a provisional amount of $26,674 related to the re-measurement of its deferred tax assets and liabilities resulting from the change in the corporate tax rate from 35% to 21% and has not adjusted the amount when completing its analysis. The Tax Act created a new requirement that Global Intangible Low-Taxed Income (i.e., GILTI) earned by controlled foreign corporations (CFCs) must be included currently in the gross income of the CFCs’ U.S. shareholder. A deduction is permitted to a domestic corporation in an amount up to 50% of the sum of the GILTI inclusion and the amount treated as a dividend because the corporation has claimed a foreign tax credit (FTC) as a result of the inclusion of the GILTI amount in income. The Company has made a policy election to record tax effects of GILTI as a period expense when incurred. 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: 2018 2017 2016 Income (Loss): U.S. $ (68,698 ) $ 48,053 $ (16,661 ) Non-U.S. (11,709 ) 39,025 (33,055 ) $ (80,407 ) $ 87,078 $ (49,716 ) The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2018 2017 2016 Current tax provision U.S. federal $ 444 $ (1,657 ) $ — U.S. state and local 2 98 (1,520 ) Non-U.S. 7,584 6,514 2,154 8,030 4,955 634 Deferred tax provision (benefit): U.S. federal (9,315 ) (172,873 ) 5,785 U.S. state and local (2,990 ) (7,775 ) (3,550 ) Non-U.S. 35,878 7,629 (12,273 ) 23,573 (173,019 ) (10,038 ) Income tax provision (benefit) $ 31,603 $ (168,064 ) $ (9,404 ) 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: 2018 2017 2016 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ (80,407 ) $ 87,078 $ (49,716 ) Statutory income tax rate 21.0 % 35.0 % 35.0 % Tax expense (benefit) using statutory income tax rate (16,886 ) 30,477 (17,401 ) State and foreign taxes (2,988 ) 8,863 (94 ) Non-deductible stock-based compensation 1,512 1,441 1,123 Other non-deductible expense 10,091 (220 ) 1,848 Change to valuation allowance 49,482 (103,212 ) 6,605 Effect of the difference in U.S. federal and local statutory rates (152 ) (2,939 ) (353 ) Impact of tax reform — (100,472 ) — Noncontrolling interests (2,674 ) (4,413 ) (1,287 ) Impact of foreign operations 1,711 (2,453 ) — Adjustment to deferred tax balances (8,865 ) — — Other, net 372 4,864 155 Income tax expense (benefit) $ 31,603 $ (168,064 ) $ (9,404 ) Effective income tax rate (39.3 )% (193.0 )% 18.9 % 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 periods 2017 and 2016 in the table above have been conformed to reflect the U.S. statutory rate. Income tax expense for the twelve months ended December 31, 2018 was $ 31,603 (associated with a pretax loss of $80,407 ) compared to an income tax benefit of $168,064 (associated with pretax income of $87,078 ) for the twelve months ended December 31, 2017 . Income tax expense in 2018 included the impact of establishing a valuation allowance primarily associated with Canadian deferred tax assets and the income tax benefit in 2017 included the impact of a release of a valuation allowance in certain jurisdictions as well as the incremental tax benefit associated with the Tax Act. Income taxes receivable were $4,388 and $4,582 at December 31, 2018 and 2017 , respectively, and were included in other current assets on the balance sheet. Income taxes payable were $10,045 and $3,810 at December 31, 2018 and 2017 , 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: 2018 2017 Deferred tax assets: Capital assets and other $ 905 $ 5,059 Net operating loss carry forwards 70,646 49,318 Interest deductions 8,911 2,026 Refinancing charge 2,926 5,578 Goodwill and intangibles 123,504 129,455 Stock compensation 2,101 1,208 Pension plan 3,872 4,165 Unrealized foreign exchange 14,645 8,653 Capital loss carry forwards 11,827 11,450 Accounting reserves 8,280 412 Gross deferred tax asset 247,617 217,324 Less: valuation allowance (68,479 ) (19,032 ) Net deferred tax assets 179,138 198,292 Deferred tax liabilities: Goodwill amortization (91,726 ) (89,727 ) Total deferred tax liabilities (91,726 ) (89,727 ) Net deferred tax asset (liability) $ 87,412 $ 108,565 Disclosed as: Deferred tax assets $ 92,741 $ 115,325 Deferred tax liabilities (5,329 ) (6,760 ) $ 87,412 $ 108,565 The Company has U.S. federal net operating loss carry forwards of $68,325 and non-U.S. net operating loss carry forwards of $153,021 . These carry forwards expire in years 2017 through 2032 . The Company also has total indefinite loss carry forwards of $122,830 . These indefinite loss carry forwards consist of $33,572 relating to the U.S. and $89,258 which are 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 $118,575 . 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, 2017, the Company maintained valuation allowance against foreign net deferred tax assets of $19,032 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, 2018, 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, 2018, the Company’s Canadian three-year cumulative pre-tax income declined compared to the period ended December 31, 2017 and the Company recorded a valuation allowance of $49,447 . 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 expense of $49,447 for the year ended December 31, 2018. The Company is permanently reinvested with respect to its foreign earnings in certain jurisdictions, and no deferred taxes have been recorded related to such earnings as the determination of the amount is not practicable. The Company currently does not intend to distribute previously taxed income under the Tax Act. Upon distribution in the future, the Company may incur state and foreign withholding taxes on such income, the amount of which is not practicable to compute. As of December 31, 2018 and 2017 , the Company recorded a liability for unrecognized tax benefits as well as applicable penalties and interest in the amount of $973 and $1,556 , respectively. As of December 31, 2018 and 2017 , accrued penalties and interest included in unrecognized tax benefits were approximately $87 and $123 , 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. 2018 2017 2016 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 1,433 $ 1,465 $ 3,605 Current year positions — 489 — Prior period positions 7 (436 ) (134 ) Settlements (314 ) — (1,374 ) Lapse of statute of limitations (239 ) (85 ) (632 ) Unrecognized tax benefits - Ending Balance $ 887 $ 1,433 $ 1,465 It is reasonably possible that the amount of unrecognized tax benefits could decrease by a range of $400 to $500 in the next twelve months as a result of expiration of certain statute of limitations. The Company is subject to taxation and files income tax returns in the U.S. federal jurisdiction and in many state and foreign jurisdictions. The U.S. Internal Revenue Service (“IRS”) concluded its review of the 2013 tax year and all years prior to 2015 are closed. The statute of limitations has also expired in non-U.S. jurisdictions through 2013.

Debt

Debt	12 Months Ended
	Dec. 31, 2018
Debt Disclosure [Abstract]
Debt	12. Debt As of December 31, the Company’s indebtedness was comprised as follows: 2018 2017 Revolving credit agreement $ 68,143 $ — 6.50% Notes due 2024 900,000 900,000 Debt issuance costs (14,036 ) (17,587 ) 954,107 882,413 Obligations under capital leases 478 706 954,585 883,119 Less: Current portion of long-term debt (356 ) (313 ) $ 954,229 $ 882,806 Interest expense related to long-term debt for the years ended December 31, 2018 , 2017 , and 2016 was $64,420 , $62,001 and $56,468 , respectively. For the twelve months ended December 31, 2016 , the Company recorded a charge for the loss on redemption of the 6.75% Notes of $33,298 , which included accrued interest, related premiums, fees and expenses, write offs of unamortized original issue premium, and unamortized debt issuance costs. For the year ended December 31, 2016 , interest expense included income of $312 , related to the amortization of the original issue premium. For the years ended December 31, 2018 , 2017 , and 2016 , interest expense included $87 , $100 and $255 , respectively, of present value adjustments for fixed deferred acquisition payments. The amortization of deferred finance costs included in interest expense were $3,193 , $3,022 and $3,022 for the years ended December 31, 2018 , 2017 , and 2016 , 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 unsecured 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, on and after May 1, 2019 , 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, 2018. Redemption of 6.75% Notes On March 23, 2016, the Company redeemed the 6.75% Notes in whole at a redemption price of 103.375% of the principal amount thereof with the proceeds from the issuance of the 6.50% Notes. Credit Agreement On May 3, 2016 MDC, Maxxcom Inc. (a subsidiary of MDC) and each of their subsidiaries party thereto entered into a second amended and restated, $325,000 senior secured revolving credit agreement due May 3, 2021 (as amended, the “Credit Agreement”) with Wells Fargo Capital Finance, LLC, as agent, 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. Capitalized terms used in this section and not otherwise defined have the meanings set forth in 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 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, subject to customary exceptions and collateralized by a portion of MDC ’ s outstanding receivable balance. The Credit Agreement includes covenants that, among other things, restrict MDC’s ability and the ability of its subsidiaries to incur or guarantee additional indebtedness; pay dividends on or redeem or repurchase the capital stock of MDC; make certain types of investments; impose limitations on dividends or other amounts from MDC’s subsidiaries; incur certain liens, sell or otherwise dispose of certain assets; enter into transactions with affiliates; 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 Company is currently in compliance with all of the terms and conditions of its Credit Agreement, and management believes, based on its current financial projections, that the Company will be in compliance with the covenants over the next twelve months. Amendment to Credit Agreement 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 (the “Amendment”) to the existing senior secured revolving credit facility, dated as of May 3, 2016 (as amended, the “Credit Agreement”), among the Company, Maxxcom Inc., a Delaware corporation, each of their subsidiaries party thereto, Wells Fargo Capital Finance, LLC, as agent (“Wells Fargo”), and the lenders from time to time party thereto. 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 addition, the Company is permitted to apply a portion of the net cash proceeds of the Kingsdale Sale to the prepayment, redemption, defeasement, purchase or other acquisition of the Company’s senior unsecured debt. In connection with the Amendment, the Company reduced the aggregate maximum amount of revolving commitments provided by the lenders under the Credit Agreement to $250.0 million from $325.0 million . At December 31, 2018 , the Company had issued $4,701 of undrawn letters of credit. At December 31, 2018 and 2017 , accounts payable included $40,271 and $41,989 , respectively, of outstanding checks. Future Principal Repayments Future principal repayments, including capital lease obligations, for the years ended December 31, and in aggregate, are as follows: Period Amount 2019 $ 356 2020 101 2021 68,164 2022 — 2023 — 2024 and thereafter 900,000 $ 968,621 Capital Leases Future minimum capital lease payments for the years ended December 31 and in aggregate, are as follows: Period Amount 2019 $ 356 2020 101 2021 21 2022 — 2023 — 2024 and thereafter — 478 Less: imputed interest (42 ) 436 Less: current portion (356 ) $ 80 Capital lease obligations at December 31 were: 2018 2017 Current $ 356 $ 313 Long-term 122 393 $ 478 $ 706

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share Capital	13. Share Capital As of December 31, 2018, we changed the presentation of our Consolidated Statements of Shareholders’ Deficit to combine the amounts in common shares and charges in excess of capital to present a combined “Common stock and other paid-in capital” as SEC Regulation S-X allows for this presentation. As such, we reclassified the prior year balances as of December 31, 2017 and 2016 to conform with the current period presentation. Authorized Share Capital The authorized share capital of the Company is as follows: Series 4 Convertible Preference Shares See Note 14 of the Notes to the Consolidated Financial Statements included herein for additional information. Class A Shares 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 is an unlimited number of Class A shares authorized, 57,517,568 and 56,371,376 Class A shares are issued and outstanding as of December 31, 2018, and 2017, respectively. Class B Shares An unlimited number, carrying 20 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 is an unlimited number of Class B shares authorized, 3,755 Class B shares are issued and outstanding as of December 31, 2018, and 2017, respectively. Employee Stock Incentive Plan As of December 31, 2018, 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, 2017 — $ — 785,085 $ 11.94 Granted 503,321 9.17 156,440 7.38 Vested (4,444 ) 10.30 (239,085 ) 14.99 Forfeited (45,965 ) 9.29 (75,500 ) 9.75 Balance at December 31, 2018 452,912 $ 9.15 626,940 $ 9.83 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. Performance based and time based awards granted in the twelve months ended December 31, 2016 had a weighted average grant date fair value of $14.00 and $12.53 , respectively. The vesting of the performance based awards is contingent upon the Company meeting a cumulative three year earnings target and continued employment through the vesting date. Once the Company defines the earnings target, the grant date is established and the Company will record the compensation expense over the vesting period. 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 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, 2018 , 2017 and 2016 was $3,583 , $7,316 and $6,272 , respectively. At December 31, 2018 , the weighted average remaining contractual life for time based and performance based awards was 1.98 and less than a year, respectively. At December 31, 2018 , the unrecognized compensation expense for performance based awards was $260 to be recognized over a weighted average period of less than a year. At December 31, 2018 , the unrecognized compensation expense for time based awards was $2,325 to be recognized over a weighted average period of 1.98 years. The following table summarizes information about share option awards: Share Option Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2017 — $ — $ — Granted 111,866 2.23 4.85 Vested — — — Forfeited — — — Exercised — — — Balance at December 31, 2018 111,866 $ 2.23 $ 4.85 We use the Black-Scholes option-pricing model to estimate the fair value of options granted. 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 vesting period of these awards is generally commensurate with the requisite service period. At December 31, 2018, the weighted average remaining contractual life for these awards was 3 years. No options were exercised during 2018. The intrinsic value of options exercised during 2017 and 2016, was $125 and $471 , respectively. The aggregate intrinsic value of options outstanding as of December 31, 2018 is nil . As of December 31, 2018, no options were exercisable. No options were granted in 2017 or 2016. At December 31, 2018 , the unrecognized compensation expense for these awards was $225 to be recognized over a weighted average period of 3 years. The cash received from the stock options exercised in 2017 and 2016 was nil and 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, 2017 327,500 $ 2.35 $ 6.60 Granted — — — Vested — — — Forfeited (76,700 ) 2.35 6.60 Exercised — — — Balance at December 31, 2018 250,800 $ 2.35 $ 6.60 We use the Black-Scholes option-pricing model to estimate the fair value of the SAR awards. 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% . 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 vesting period of awards granted is generally commensurate with the requisite service period. At December 31, 2018, the weighted average remaining contractual life for these awards was 1.08 years. No SAR awards were granted in 2016. As of December 31, 2018, no SAR awards were exercisable. As of December 31, 2018, there were no SAR awards that were vested. The aggregate intrinsic value of the SAR awards outstanding as of December 31, 2018 is nil . At December 31, 2018, the unrecognized compensation expense for these awards was $213 to be recognized over a weighted average period of 1.08 years. For the years ended December 31, 2018, 2017 and 2016, $5,892 , $5,335 , and $5,808 was recognized in stock compensation related to all stock compensation awards, respectively. The related income tax benefit for the years ended December 31, 2018, 2017 and 2016 was $472 , $1,401 , and $2,030 , respectively.

Convertible Preference Shares (

Convertible Preference Shares (Notes)	12 Months Ended
	Dec. 31, 2018
Equity [Abstract]
Convertible Preference Shares	Convertible Preference Shares On March 7, 2017 (the “Issue Date”), the Company issued 95,000 newly created 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. Except as required by law, the Preference Shares do not have voting rights, and are not redeemable at the option of the Purchaser. The holders of the Preference Shares have the right to convert their Preference Shares in whole at any time and from time to time, and in part at any time and from time to time after the ninetieth day following the original issuance date of the Preference Shares, 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 per share preference of each Preference Share is $1,000 . The initial Conversion Price is $10.00 per 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. In connection with the anti-dilution protection provision associated with the issuance of equity securities on March 14, 2019 (see Note 23), the Conversion Price has been reduced to $7.42 from $10.00 per Preference Share. The Preference Shares’ liquidation preference accretes at 8.0% per annum, compounded quarterly until the five-year anniversary of the Issue Date. For the twelve months ended 2018 and 2017 , the Preference Shares accreted at a monthly rate of approximately $7.55 and $6.97 per Preference Share, for total accretion of $8,355 and $6,352 , respectively, bringing the aggregate liquidation preference to $ 109,707 as of December 31, 2018 . The accretion is considered in the calculation of net income (loss) attributable to MDC Partners Inc. common shareholders. Holders of the 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 Preference Shares. The 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 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 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 Preference Shares for cash at the greater of their liquidation preference plus accrued and unpaid dividends or their as-converted value.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Fair Value Measurements	15. 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 inputs 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 measured at fair value on a recurring basis at December 31: 2018 2017 Carrying Amount Fair Value Carrying Amount Fair Value Liabilities: 6.50% Senior Notes due 2024 $ 900,000 $ 834,750 $ 900,000 $ 904,500 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 are 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 6 of the Notes to the Consolidated Financial Statements for additional information regarding contingent deferred acquisition consideration. At December 31, 2018 and 2017 , 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 and intangible assets. Accordingly, these assets are not measured and adjusted to fair value on an ongoing basis but are subject to periodic evaluations for potential impairment. See Note 2 and 10 of the Notes to the Consolidated Financial Statements for information related to the measurement of the fair value of goodwill (a Level 3 fair value assessment).

Segment Information

Segment Information	12 Months Ended
	Dec. 31, 2018
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. Effective January 1, 2019, the Executive Committee assumed the role and responsibilities of the Chief Executive Officer until the appointment of a successor which occurred on March 18, 2019. See Note 1 of the Notes to the Consolidated Financial Statements included herein for additional information. Once operating segments are identified, the Company performs an analysis to determine if aggregation of operating segments is applicable. This determination is based upon a quantitative analysis of the expected and historic average long-term profitability for each operating segment, together with a qualitative assessment to determine if operating segments have similar operating characteristics. Due to changes in the Company’s internal management and reporting structure during 2018, reportable segment results for 2017 and prior periods presented have been recast to reflect the reclassification of certain businesses between segments. The changes were as follows: • Source Marketing, previously within the All Other category, was included within the Doner operating segment, which is aggregated into the Global Integrated Agencies reportable segment; • Yamamoto, previously within the All Other category, was operationally merged with Civilian and is now included within the Domestic Creative Agencies reportable segment; • Bruce Mau Design, Hello Design and Northstar Research Partners, previously within the All Other category, and Varick Media Management, previously within the Media Services reportable segment, were included into a newly-formed operating segment, Yes & Company, which is aggregated within the Media Services reportable segment. Also in 2018, Forsman & Bodenfors and kbs+, both within the Global Integrated Agencies reportable segment, merged under the Forsman & Bodenfors name. 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 five global, integrated operating segments (72andSunny, Anomaly, Crispin Porter Bogusky, Doner 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 five operating segments that are national advertising agencies (Colle + McVoy, Laird + Partners, Mono Advertising, Union and Yamamoto) 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 profitability 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 five operating segments that are each communications agencies (Allison & Partners, HL Group Partners, Hunter PR, KWT Global (formerly Kwittken), 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 profitability 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 two operating segments (MDC Media Partners and Yes & Company). These operating segments perform media buying and planning as their 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, Instrument, Redscout, 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. Years Ended December 31, 2018 2017 2016 Revenue: Global Integrated Agencies $ 698,872 $ 797,347 $ 712,793 Domestic Creative Agencies 102,063 104,417 97,199 Specialist Communications 179,065 172,565 170,285 Media Services 140,753 166,216 157,696 All Other 355,450 273,234 247,812 Total $ 1,476,203 $ 1,513,779 $ 1,385,785 Segment operating income (loss): Global Integrated Agencies $ 44,868 $ 71,857 $ 59,193 Domestic Creative Agencies 18,552 19,333 18,089 Specialist Communications 18,629 20,728 1,940 Media Services (51,196 ) 13,126 5,554 All Other 34,000 47,771 7,773 Corporate (55,157 ) (40,856 ) (44,118 ) Total $ 9,696 $ 131,959 $ 48,431 Other Income (Expense): Interest expense and finance charges, net (67,075 ) (64,364 ) (65,050 ) Foreign exchange transaction gain (loss) (23,258 ) 18,137 (213 ) Loss on redemption of Notes — — (33,298 ) Other, net 230 1,346 414 Income (loss) before income taxes and equity in earnings (losses) of non-consolidated affiliates (80,407 ) 87,078 (49,716 ) Income tax expense (benefit) 31,603 (168,064 ) (9,404 ) Income (loss) before equity in earnings (losses) of non-consolidated affiliates (112,010 ) 255,142 (40,312 ) Equity in earnings (losses) of non-consolidated affiliates 62 2,081 (309 ) Net income (loss) (111,948 ) 257,223 (40,621 ) Net income attributable to the noncontrolling interest (11,785 ) (15,375 ) (5,218 ) Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Years Ended December 31, 2018 2017 2016 Depreciation and amortization: Global Integrated Agencies $ 23,571 $ 23,831 $ 21,555 Domestic Creative Agencies 1,583 1,582 1,811 Specialist Communications 4,252 4,714 6,637 Media Services 3,119 4,052 6,091 All Other 12,909 8,197 8,768 Corporate 762 1,098 1,584 Total $ 46,196 $ 43,474 $ 46,446 Stock-based compensation: Global Integrated Agencies $ 8,521 $ 15,225 $ 12,177 Domestic Creative Agencies 1,100 887 651 Specialist Communications 714 2,954 3,629 Media Services 318 656 318 All Other 3,104 2,494 1,703 Corporate 4,659 2,134 2,525 Total $ 18,416 $ 24,350 $ 21,003 Capital expenditures: Global Integrated Agencies $ 10,088 $ 20,760 $ 16,486 Domestic Creative Agencies 951 1,168 1,153 Specialist Communications 3,618 1,288 2,741 Media Services 966 3,842 5,266 All Other 4,574 5,877 3,753 Corporate 67 23 33 Total $ 20,264 $ 32,958 $ 29,432 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 2018 $ 76,781 $ 4,779 $ 6,629 $ 88,189 2017 $ 77,163 $ 5,638 $ 7,505 $ 90,306 Goodwill and Intangible Assets 2018 $ 679,344 $ 61,748 $ 67,628 $ 808,720 2017 $ 706,241 $ 127,014 $ 73,285 $ 906,540 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: 2018 $ 1,153,192 $ 124,000 $ 199,011 $ 1,476,203 2017 $ 1,172,364 $ 123,092 $ 218,323 $ 1,513,779 2016 $ 1,103,714 $ 124,101 $ 157,970 $ 1,385,785

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2018
Related Party Transactions [Abstract]
Related Party Transactions	17. Related Party Transaction Scott L. Kauffman is Chairman of the Company’s Board of Directors, and is the former Chief Executive Officer of the Company. His daughter, Sarah Kauffman, has been employed by Partner Firm Forsman & Bodenfors since July 2011, and currently acts as Director of Operations, Attention Partners. In 2018 and 2017 , her total compensation, including salary, bonus and other benefits, totaled approximately $172 and $155 , respectively. Her compensation is commensurate with that of her peers.

Commitments, Contingencies and

Commitments, Contingencies and Guarantees	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments, Contingencies and Guarantees	. Commitments, Contingencies and Guarantees Legal Proceedings . The Company’s operating entities are involved in legal proceedings of various types. While any litigation contains an element of uncertainty, the Company has no reason to believe that the outcome of such proceedings or claims will have a material adverse effect on the financial condition or results of operations of the Company. Dismissal of Class Action Litigation . On August 7, 2015, Roberto Paniccia issued a Statement of Claim in the Ontario Superior Court of Justice in the City of Brantford, Ontario seeking to certify a class action suit naming the following as defendants: MDC, former CEO Miles S. Nadal, former CAO Michael C. Sabatino, CFO David Doft and BDO U.S.A. LLP. The Plaintiff alleged violations of section 138.1 of the Ontario Securities Act (and equivalent legislation in other Canadian provinces and territories) as well as common law misrepresentation based on allegedly materially false and misleading statements in the Company’s public statements, as well as omitting to disclose material facts with respect to the SEC investigation. On June 4, 2018, the Court dismissed (with costs) the putative class members’ motion for leave to proceed with the Plaintiff’s claims for misrepresentations of material facts pursuant to the Ontario Securities Act. Following the Court’s decision, on June 18, 2018, the Plaintiff, MDC and each of the other defendants consented to the dismissal of the action with prejudice (and without costs). In July 2018, the Court entered a final order approving the dismissal of this claim. Closing of Antitrust Investigation. In 2016, one of the Company’s subsidiary agencies received a subpoena from the U.S. Department of Justice Antitrust Division (the “DOJ”) concerning the DOJ’s ongoing investigation of production bidding practices in the advertising industry. The Company and its subsidiary fully cooperated with this confidential investigation. By letter dated November 5, 2018 (received by the Company’s counsel on November 12, 2018), the DOJ confirmed that the foregoing investigation had been closed. The DOJ did not bring any charges against the Company, its subsidiary or any of their respective employees. Deferred Acquisition Consideration and Option to Purchase. See Note 6 of the Notes to the Consolidated Financial Statements included herein for additional information regarding potential payments associated with deferred acquisition consideration and Note 8 for 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, 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 these losses are probable and estimable. Commitments . At December 31, 2018 , the Company had $4,701 of undrawn letters of credit. In addition, the Company has commitments to fund investments in an aggregate amount of $40 . Leases . The Company and its subsidiaries lease certain facilities and equipment. For the years ended December 31, 2018 , 2017 , and 2016 , gross premises rental expense amounted to $65,093 , $64,086 , and $56,725 , respectively, which was reduced by sublease income of $3,671 , $2,797 , and $3,027 , respectively. Certain of our office facilities’ leases contain escalation clauses, lease renewals and lease incentives, including periods of free rent and allowances from landlords to be applied against necessary leasehold improvements. In circumstances where the exercise of renewal options is reasonably assured at the inception of the lease, the renewal period is included in the determination of the lease term. Where leases contain escalation clauses or other concessions, the impact of such adjustments is recognized on a straight-line basis over the minimum lease period. Minimum rental commitments for the rental of office and production premises and equipment under non-cancellable leases net of sublease income, some of which provide for rental adjustments due to increased property taxes and operating costs, for the years ending December 31, 2019 and thereafter, are as follows: Period Amount 2019 $ 58,015 2020 55,211 2021 45,974 2022 40,387 2023 38,348 2024 and thereafter 107,975 $ 345,910 At December 31, 2018 , the total future cash to be received on sublease income is $15,930 .

New Accounting Pronouncements

New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Pronouncements	. New Accounting Pronouncements Adopted In The Current Reporting Period Effective January 1, 2018, the Company adopted ASC 606. ASC 606 was applied using the modified retrospective method, with the cumulative effect of the initial adoption being recognized as an adjustment to opening retained earnings at January 1, 2018. As a result, comparative prior periods have not been adjusted and continue to be reported under ASC 605. The following represents changes to the Company’s policies resulting from the adoption of ASC 606: i. Under the guidance in effect through December 31, 2017, performance incentives were recognized in revenue when specific quantitative goals were achieved, or when the Company’s performance against qualitative goals was determined by the client. Under ASC 606, the Company now estimates the amount of the incentive that will be earned at the inception of the contract and recognizes such incentive over the term of the contract. This results in an acceleration of revenue recognition for certain contract incentives compared to ASC 605. ii. Under the guidance in effect through December 31, 2017, non-refundable retainer fees were generally recognized on a straight-line basis over the term of the specific customer arrangement. Under ASC 606, an input method is typically used to measure progress and recognize revenue for these types of arrangements. This resulted in both the deferral and acceleration of revenue recognition in certain instances. iii. In certain client arrangements, the Company records revenue as a principal and includes within revenue certain third-party-pass-through and out-of-pocket costs, which are billed to clients in connection with the services provided. In other arrangements, the Company acts as an agent and records revenue equal to the net amount retained. The adoption of ASC 606 resulted in certain arrangements previously being accounted for as principal, now being accounted for as agent. As a result of these changes, the Company recorded a cumulative effect adjustment to increase opening accumulated deficit at January 1, 2018 by $1,170 . The following table summarizes the impact of adoption of ASC 606 on the Consolidated Statement of Operations during the twelve months ended December 31, 2018 : Twelve Months Ended December 31, 2018 As Reported Adjustments Adjusted to Exclude Adoption of ASC 606 Revenue - Services $ 1,476,203 $ 51,636 $ 1,527,839 Costs of services sold $ 991,198 $ 62,358 $ 1,053,556 Operating income (loss) $ 9,696 $ (10,722 ) $ (1,026 ) Net loss attributable to MDC Partners Inc. common shareholders $ (132,088 ) $ (6,883 ) $ (138,971 ) Loss per common share - basic and diluted $ (2.31 ) $ (0.12 ) $ (2.43 ) The impact on the Consolidated Balance Sheet and Consolidated Statement of Shareholders’ Deficit as of and for the twelve months ended December 31, 2018 was immaterial. There was no effect on the Consolidated Statement of Comprehensive Income (Loss) and the Consolidated Statement of Cash Flows for the twelve months ended December 31, 2018 and 2017. In March 2018, the FASB issued ASU 2018-05, Income Taxes (Topic 740) - Amendments to SEC Paragraphs Pursuant to SEC Staff Accounting Bulletin No. 119, which provides guidance on the accounting for tax on the global intangible low-taxed income (“GILTI”) provisions of the Tax Cuts and Jobs Act (the “Act”). The GILTI provisions impose a tax on foreign income in excess of a deemed return on tangible assets of foreign corporations. The guidance indicates that either accounting for deferred taxes related to GILTI inclusions or treating any taxes on GILTI inclusions as period cost are both acceptable methods subject to an accounting policy election. The Company has adopted this standard effective January 1, 2018 and has made a policy election to record tax effects of GILTI as an expense in the period incurred. For the twelve months ending December 31, 2018 GILTI resulted in additional income tax expense of $710 . For more information on the adoption of the Act, see Note 11. In May 2017, the FASB issued Accounting Standards Update (“ASU”) 2017-09, Compensation - Stock Compensation: Scope of Modification Accounting, which provides guidance concerning which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting in ASC 718. This guidance is effective for annual and interim periods beginning after December 15, 2017. Amendments in this ASU are applied prospectively to any award modified on or after the adoption date. The Company adopted this guidance on January 1, 2018. The impact on the Company’s consolidated statement of financial position and results of operations was not material. In March 2017, the FASB issued ASU 2017-07, Compensation - Retirement Benefits, which requires the presentation of the service cost component of the net periodic pension and postretirement benefits costs in the same line item in the statement of operations as other compensation costs arising from services rendered by the pertinent employees during the period. The other components of the net periodic pension and postretirement benefits costs are required to be presented as non-operating expenses in the statement of operations. This guidance is effective for annual periods beginning after December 15, 2017. The Company adopted this guidance on January 1, 2018. The impact on the Company’s consolidated statement of financial position and results of operations was not material. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230) which requires that the Consolidated Statement of Cash Flows present the change during the period in the total cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. We have adopted this amended guidance retrospectively as of the year ended December 31, 2018. The Consolidated Statements of Cash Flows now reflect the inclusion and activity of restricted cash balances of $3.9 million (classified within Assets held for sale in the Consolidated Balance Sheet), $4.6 million , and $5.3 million as of December 31, 2018, 2017, and 2016 respectively. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows. This new guidance is intended to reduce diversity in practice regarding the classification of certain transactions in the statement of cash flows. This guidance is effective January 1, 2018 and requires a retrospective transition method. Prior to the Company’s adoption on January 1, 2018, all cash outflows for contingent consideration were classified as a financing activity. Effective January 1, 2018, the Company is now required to classify any cash payments made soon after the acquisition date of a business to settle a contingent consideration liability as cash outflows for investing activities. Cash payments which are not made soon after the acquisition date of a business to settle a contingent consideration liability are separated and classified as cash outflows for financing activities up to the amount of the contingent consideration liability recognized at the acquisition date and as cash outflows from operating activities for any excess. As a result, $29,141 , $42,790 , and $44,914 of an acquisition-related contingent consideration payment of $61,313 , $99,873 , and $135,693 , which was in excess of the liability initially recognized at the acquisition date, has been classified as a cash outflow within net cash provided by operating activities in the accompanying consolidated statement of cash flows for the twelve months ended December 31, 2018 , 2017, and 2016 respectively. There was no impact on the Company’s consolidated statement of financial position and results of operations. In January 2016, the FASB issued ASU 2016-01, Financial Instruments - Overall: Recognition and Measurement of Financial Assets and Liabilities , which will require equity investments, except equity method investments, to be measured at fair value and any changes in fair value will be recognized in results of operations. This guidance is effective for annual and interim periods beginning after December 15, 2017. Additionally, this guidance provides for the recognition of the cumulative effect of retrospective application of the new standard in the period of initial application. The Company adopted this guidance on January 1, 2018. The impact on the Company’s consolidated statement of financial position and results of operations was not material. To be Adopted in Future Reporting Periods In February 2016, the FASB issued ASU 2016-02, Leases. The new guidance will require lessees to recognize a right-to-use asset and lease liability for most of its leases with a term of more than twelve months, including those classified as operating leases. The new guidance also requires additional quantitative and qualitative disclosures. This guidance will be effective for annual periods beginning after December 15, 2018, with early adoption permitted. The FASB issued ASU No. 2018-10 “Codification Improvements to Topic 842, Leases” and ASU No. 2018-11 “Leases (Topic 842) Targeted Improvements” in July 2018. ASU 2018-10 provides certain amendments that affect narrow aspects of the guidance issued in ASU 2016-02. ASU 2018-11 provides an optional transition method allowing entities to apply the new lease standard at the adoption date with a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption (modified retrospective approach) as opposed to restating prior period consolidated financial statements. The Company elected to adopt the standard on January 1, 2019, which is the date of initial application, using the modified retrospective adoption method. The Company has implemented a new system to support the Company’s financial reporting and disclosure under the new standard and is finalizing its new accounting policies, processes and internal controls. The Company is in the process of quantifying the full impact of the application of the new guidance; however, it expects that the recognition of a right-to-use asset and lease liability for operating leases will have a significant impact on its balance sheet.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Dec. 31, 2018
Retirement Benefits [Abstract]
Employee Benefit Plans	A subsidiary acquired in 2012 sponsors a defined benefit plan. The benefits under the defined benefit plan are based on each employee’s years of service and compensation. Effective February 28, 2007, the plan was closed to all new entrants, and effective February 28, 2010, all benefit accruals under the plan were 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 Pension Pension 2018 2017 2016 Service cost $ — $ — $ — Interest cost on benefit obligation 1,641 1,725 1,855 Expected return on plan assets (1,948 ) (1,830 ) (1,863 ) Curtailment and settlements 1,039 — 929 Amortization of actuarial losses 258 222 137 Net periodic benefit cost $ 990 $ 117 $ 1,058 The above costs are included within Other income, net on the Consolidated Statements of Operations. The following weighted average assumptions were used to determine net periodic costs at December 31: Pension Pension Pension 2018 2017 2016 Discount rate 3.83 % 4.32 % 4.69 % Expected return on plan assets 7.00 % 7.40 % 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 Pension 2018 2017 Current year actuarial (gain) loss $ (520 ) $ 1,558 Amortization of actuarial loss (258 ) (222 ) Total recognized in other comprehensive (income) loss $ (778 ) $ 1,336 Total recognized in net periodic benefit cost and other comprehensive (income) loss $ 212 $ 1,453 The following table summarizes the change in benefit obligations and fair values of plan assets for the years ended December 31: 2018 2017 Change in benefit obligation: Benefit obligation, Beginning balance $ 43,750 $ 40,722 Interest Cost 1,641 1,725 Actuarial losses (3,522 ) 3,088 Benefits paid (3,931 ) (1,785 ) Benefit obligation, Ending balance 37,938 43,750 Change in plan assets: Fair value of plan assets, Beginning balance 27,977 24,482 Actual return on plan assets (2,093 ) 3,360 Employer contributions 1,228 1,920 Benefits paid (3,931 ) (1,785 ) Fair value of plan assets, Ending balance 23,181 27,977 Unfunded status $ 14,757 $ 15,773 Amounts recognized in the balance sheet at December 31 consist of the following: Pension Pension 2018 2017 Non-current liability $ 14,757 $ 15,773 Net amount recognized $ 14,757 $ 15,773 Amounts recognized in Accumulated Other Comprehensive Loss before income taxes consists of the following components for the years ended December 31: Pension Pension 2018 2017 Accumulated net actuarial losses $ 12,878 $ 13,656 Amount recognized $ 12,878 $ 13,656 In 2019, the Company estimates that it will recognize $266 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 Pension 2018 2017 Discount rate 4.42 % 3.83 % Rate of compensation increase N/A N/A The discount rate assumptions at December 31, 2018 and 2017 were determined independently. A yield curve was produced for a universe containing the majority of U.S.-issued AA-graded corporate bonds, all of which were non-callable (or callable with make-whole provisions). The discount rate was developed as the level equivalent rate that would produce the same present value as that using spot rates aligned with the projected benefit payments. Fair Value of Plan Assets and Investment Strategy The fair value of the plan assets as of December 31 is as follows: 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 $ — $ — December 31, 2017 Level 1 Level 2 Level 3 Asset Category: Money Market Fund – Short Term Investments $ 1,695 $ 1,695 $ — $ — Mutual Funds 26,282 26,282 — — Total $ 27,977 $ 27,977 $ — $ — The pension plans weighted-average asset allocation for the years ended December 31, 2018 , and 2017 are as follows: Target Allocation Actual Allocation Actual Allocation 2018 2018 2017 Asset Category: Equity Securities 65.0 % 67.0 % 68.9 % Debt Securities 30.0 % 25.5 % 25.0 % Cash/Cash Equivalents and Short Term Investments 5.0 % 7.5 % 6.1 % 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 primarily located in the United States, as well as a smaller percentage invested in large-cap and mid-cap companies located outside of 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 2018, the Company contributed $1,228 to the pension plan. The Company estimates that it will make approximately $1,156 in contributions to the pension plan in 2019. 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 2019 $ 1,690 2020 1,857 2021 1,848 2022 1,912 2023 2,139 2024 – 2027 11,047

Changes in Accumulated Other Co

Changes in Accumulated Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2018
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, 2016 $ (12,320 ) $ 10,496 $ (1,824 ) Other comprehensive income before reclassifications — 1,206 1,206 Amounts reclassified from accumulated other comprehensive income (loss) (1,336 ) — (1,336 ) Other comprehensive income (loss) (1,336 ) 1,206 (130 ) 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 (loss) (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

Quarterly Results of Operations

Quarterly Results of Operations (Unaudited)	12 Months Ended
	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Results of Operations (Unaudited)	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: 2018 $ 326,968 $ 379,743 $ 375,830 $ 393,662 2017 $ 344,700 $ 390,532 $ 375,800 $ 402,747 Cost of services sold: 2018 $ 243,030 $ 253,390 $ 238,690 $ 256,088 2017 $ 237,563 $ 267,822 $ 249,418 $ 268,673 Net Income (loss): 2018 $ (28,519 ) $ 5,951 $ (13,667 ) $ (75,713 ) 2017 $ (9,683 ) $ 13,467 $ 21,984 $ 231,455 Net income (loss) attributable to MDC Partners Inc.: 2018 $ (29,416 ) $ 3,406 $ (16,125 ) $ (81,598 ) 2017 $ (10,566 ) $ 11,253 $ 18,493 $ 222,668 Income (loss) per common share: Basic 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) 2017 $ (0.21 ) $ 0.14 $ 0.25 $ 3.33 Diluted 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) 2017 $ (0.21 ) $ 0.14 $ 0.24 $ 3.30 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 2018 and 2017 included a foreign exchange loss of $13,324 and $660 , respectively. • The fourth quarter of 2018 and 2017 included stock-based compensation charges of $1,534 and $7,480 , respectively. • The fourth quarter of 2018 and 2017 included changes in deferred acquisition resulting in income of $8,979 and $18,173 , respectively. • The fourth quarter of 2018 included goodwill and other asset impairment charges of $56,732 and the third and fourth quarter of 2017 included goodwill impairment charges of $29,631 and $18,893 , respectively. • The fourth quarter of 2018 included income tax expense related to the establishment of the Company’s valuation allowance of $49,447 . The fourth quarter of 2017 included income tax benefit of $226,466 relating to the decrease to the valuation allowance.

VALUATION AND QUALIFYING ACCOUN

VALUATION AND QUALIFYING ACCOUNTS	12 Months Ended
	Dec. 31, 2014
SEC Schedule, 12-09, Valuation and Qualifying Accounts [Abstract]
Schedule II - Valuation and Qualifying Accounts	SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, (Dollars in Thousands) Column A Column B Column C Column D Column E Column F Description Balance at Charged to Removal of Uncollectible Receivables Translation Adjustments Balance at Valuation accounts deducted from assets to which they apply – allowance for doubtful accounts: December 31, 2018 $ 2,453 $ 1,538 $ (1,795 ) $ (317 ) $ 1,879 December 31, 2017 $ 1,523 $ 1,989 $ (924 ) $ (135 ) $ 2,453 December 31, 2016 $ 1,306 $ 1,053 $ (830 ) $ (6 ) $ 1,523 Schedule II — 2 of 2 MDC PARTNERS INC. & SUBSIDIARIES SCHEDULE II — VALUATION AND QUALIFYING ACCOUNTS For the Three Years Ended December 31, (Dollars in Thousands) Column A Column B Column C Column D Column E Column F Description Balance at Charged to Other Translation Adjustments Balance at Valuation accounts deducted from assets to which they apply – valuation allowance for deferred income taxes: December 31, 2018 $ 19,032 $ 49,447 $ — $ — $ 68,479 December 31, 2017 $ 248,867 $ (230,358 ) $ 4,108 $ (3,585 ) $ 19,032 December 31, 2016 $ 247,967 $ 6,605 $ (6,032 ) $ 327 $ 248,867 (b) Exhibits The exhibits listed on the accompanying Exhibits Index are filed as a part of this report.

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Notes)	12 Months Ended
	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Events [Text Block]	23. Subsequent Events On March 14, 2019 (the “Issue Date”), the Company entered into a securities purchase agreement with Stagwell Holdings, an affiliate of Stagwell, pursuant to which Stagwell Holdings agreed to purchase, (i) 14,285,714 newly authorized Class A shares for $3.50 per share for an aggregate purchase price of $50 million and (ii) 50,000 newly authorized Series 6 convertible preference shares (“Series 6 Preference Shares”) for an aggregate purchase price of $50 million . 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 after 1.00 year following the original issuance date of the Preference Shares, 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 per share preference of each Series 6 Preference Share is $1,000 . The initial Conversion Price is $5.00 per 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 Issue Date. 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 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. Subject to certain limitations, the Series 6 Preference Shares are not convertible into Class A Shares to the extent upon conversion the holder will beneficially hold more than 19.9% of the Company’s outstanding common shares or voting power. In the event that such restrictions would prevent the conversion of any Series 6 Preference Shares, such Series 6 Preference Shares will be converted into a separate newly authorized series of convertible preference shares of the Company, the Series 7 convertible preference shares (the “Alternative Preference Shares”), at the same conversion rate at which the Series 6 Preference Shares would convert into Class A Shares. The Alternative Preference Shares, in turn, are convertible into Class A Shares on a One -to-one basis, subject to certain conversion rate adjustments. Series 6 Preference Shares or Alternative Preference Shares will not entitle their holders to vote in the election of directors and, other than as required by applicable law, holders of the Series 6 Preference Shares will not have voting rights.

Significant Accounting Polici_2

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Accounting Policies [Abstract]
Accounting Changes [Text Block]	:
Subsidiary and Equity Investment Stock Transaction, Policy [Policy Text Block]	in any period. 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 additional paid-in capital. 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 resul
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.
Reclassifications [Text Block]	Reclassifications. Certain reclassifications have been made to the prior period consolidated financial statements to conform to the current period presentation. Additionally, certain changes to presentation have been made. The Company changed its presentation of net income allocated to convertible preference shareholders. In the Company’s Form 10-K for the year ended December 31, 2017, this amount was presented in the Income (Loss) per Common Share footnote and not on the Consolidated Statements of Operations. In connection with the presentation of the Form 10-K for the year ended December 31, 2018, the Company changed the 2017 Consolidated Statement of Operations to include the net income allocated to convertible preference shares, which was previously disclosed in footnote 3 of the December 31, 2017 financial statements.
Use of Estimates	Use of Estimates . The preparation of consolidated financial statements in conformity with U.S. 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.
Fair Value Measurement		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 Risk, 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, 2018 and 2017 .
Cash and Cash Equivalents	Cash and Cash Equivalents . The Company’s cash equivalents are primarily comprised of investments in overnight interest-bearing deposits, and 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.
Cash in Trust, Policy [Policy Text Block]	Cash in Trust. A subsidiary of the Company holds restricted cash in trust accounts related to funds received on behalf of clients. Such amounts are held in escrow under depositary service agreements and distributed at the direction of the clients. The funds are presented as a corresponding liability on the balance sheet.
Premiums Receivable, Allowance for Doubtful Accounts, Estimation Methodology	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.
Property, Plant and Equipment	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.
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.
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.
Cost Method 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, 2018 and 2017 was $8,072 and $9,527 , 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 effective January 1, 2018. 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 Intangible Assets, Goodwill	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 tradename) 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 2018 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 and demand trends and appropriate discount rates based on a reporting units 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. We performed the quantitative impairment test in 2018. See Note 10 for additional information regarding the Company’s impairment test and impairment charges recognized. Indefinite-lived intangible assets are primarily evaluated on an annual basis, generally in conjunction with the Company’s evaluation of goodwill balances.
Intangible Assets, Finite-Lived	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 recover
Deferred Taxes
Business Combinations	her 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 trade names. In executing the Company’s overall acquisition strategy, one of the primary drivers in identifying and executing a specific transaction is the existence of, or the ability to, expand the existing client relationships. The expected benefits of the Company’s acquisitions are typically shared across multiple agen
Redeemable Noncontrolling Interest	n
Variable Interest Entity	s of operations.
Guarantees, Indemnifications and Warranties
Revenue Recognition	Reven
Cost Of Services Sold	. Cost of Services Sold . Cost of services sold primarily consists of staff costs, and does not include depreciation charges
Interest Expense	or 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.
Share-based Compensation, Option and Incentive Plans	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. See Note 11 of the Notes to the Consolidated Financial Statements included herein for information related to the 2017 Tax Cuts and Jobs Act (the “Tax Act”) enacted into law on December 22, 2017, and Staff Accounting Bulletin No. 118, Income Tax Accounting Implications of the Tax Cuts and Jobs Act (“SAB 118”) issued by the SEC in December 2017. 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 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-ba
Pension and Other Postretirement Plans	tion. Retirement Costs . Several of the Company’s U.S. and Canadian 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 $9,810 , $10,124 and $10,026 for the years ended December 31, 2018 , 2017 , and 2016 , respectively. The Company also has a defined benefit pension
Earnings Per 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 restri
Foreign Currency Transactions and Translations	ipate in losses. Foreign Currency Translation . The functional currency of the Company is the Canadian dollar; however, it has decided to use U.S. dollars as its reporting currency for consolidated reporting purposes. Generally, the Company’s subsidiaries use their local currency as their functional currency. Accordingly, the currency impacts of the translation of the Consolidated Balance Sheets of the Company and its non-U.S. dollar based subsidiaries to U.S. dollar statements are included as cumulative translation adjustments in accumulated other comprehensive income (loss). Translation of intercompany debt, which is not intended to be repaid, is included in cumulative translation adjustments. Cumulative translation adjustments are not included in net earnings 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. The balance sheets of non-U.S. dollar based subsidiaries are translated at the period end rate. The Consolidated Statements of Operating 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 co
Derivatives, Reporting of Derivative Activity	prehensive income (loss).

Significant Accounting Polici_3

Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Redeemable Noncontrolling Interest	The following table presents changes in redeemable noncontrolling interests as of December 31, 2018 and 2017 : 2018 2017 Beginning Balance $ 62,886 $ 60,180 Redemptions (11,943 ) (910 ) Granted — 1,666 Changes in redemption value 1,067 1,498 Currency translation adjustments (464 ) 452 Ending balance $ 51,546 $ 62,886	s

Revenue (Tables)

Revenue (Tables)	12 Months Ended
	Dec. 31, 2018
Industry Vertical [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Table Text Block]	The following table presents revenue disaggregated by client industry vertical for the twelve months ended December 31, 2018, 2017, and 2016 and the impact of adoption of ASC 606: Twelve Months Ended December 31, 2018 2017 2016 Industry Reportable Segment As reported Adjustment to exclude impact of Adoption of ASC 606 Adjusted Food & Beverage All $ 313,368 $ 7,064 $ 320,432 $ 313,786 $ 266,600 Retail All 152,552 (2,683 ) 149,869 178,152 182,428 Consumer Products All 162,524 585 163,109 162,307 147,849 Communications All 178,410 25,957 204,367 208,701 160,064 Automotive All 88,807 8,587 97,394 127,023 129,352 Technology All 104,479 38 104,517 99,325 109,309 Healthcare All 127,547 507 128,054 124,261 115,159 Financials All 110,069 146 110,215 104,713 85,480 Transportation and Travel/Lodging All 86,419 2,461 88,880 56,955 58,298 Other All 152,028 8,974 161,002 138,556 131,246 $ 1,476,203 $ 51,636 $ 1,527,839 $ 1,513,779 $ 1,385,785
By Location [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Table Text Block]	The following table presents revenue disaggregated by geography for the twelve months ended December 31, 2018, 2017, and 2016 and the impact of adoption of ASC 606: Twelve Months Ended December 31, 2018 2017 2016 Geographic Location Reportable Segment As reported Adjustment to exclude impact of Adoption of ASC 606 Adjusted United States All $ 1,153,192 $ 20,699 $ 1,173,891 $ 1,172,364 $ 1,103,714 Canada All 124,000 (1,288 ) 122,712 123,092 124,101 Other All, Excluding Domestic Creative Agencies 199,011 32,225 231,236 218,323 157,970 $ 1,476,203 $ 51,636 $ 1,527,839 $ 1,513,779 $ 1,385,785

Loss per Common Share (Tables)

Loss per Common Share (Tables)	12 Months Ended
	Dec. 31, 2018
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 for the years ended December 31: 2018 2017 2016 Numerator: Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Accretion on convertible preference shares (8,355 ) (6,352 ) — Net income allocated to convertible preference shares — (29,902 ) — Net income (loss) attributable to MDC Partners Inc. common shareholders (132,088 ) 205,594 (45,839 ) Adjustment to net income allocated to convertible preference shares — 106 — Net income (loss) attributable to MDC Partners Inc. common shareholders $ (132,088 ) $ 205,700 $ (45,839 ) Denominator: Basic weighted average number of common shares outstanding 57,218,994 55,255,797 51,345,807 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 57,218,994 55,481,786 51,345,807 Net income (loss) attributable to MDC Partners Inc. common shareholders per common share: Basic $ (2.31 ) $ 3.72 $ (0.89 ) Diluted $ (2.31 ) $ 3.71 $ (0.89 )

Deferred Acquisition Consider_2

Deferred Acquisition Considerations (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2018 and 2017. 2018 2017 Beginning balance of contingent payments $ 119,086 $ 224,754 Payments (1) (54,947 ) (110,234 ) Additions - acquisition and step-up transactions 14,943 — Redemption value adjustments (2) 3,512 3,273 Foreign translation adjustment 4 1,293 Ending balance of contingent payments $ 82,598 $ 119,086 Fixed payments (3) 1,097 3,340 $ 83,695 $ 122,426 (1) For the twelve months ended December 31, 2017 , payments include $28,727 of deferred acquisition consideration settled through the issuance of 3,353,939 MDC Class A subordinate voting shares in lieu of cash. (2) Redemption value adjustments are fair value changes from the Company’s initial estimates of deferred acquisition payments, including the accretion of present value 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. (3) The Company made $6,366 in fixed payments for the twelve months ended December 31, 2018 . The following table presents the impact to the Company’s statement of operations due to redemption value adjustments for the twelve months ended December 31, 2018 and 2017: 2018 2017 Income attributable to fair value adjustments $ (3,679 ) $ (6,021 ) Stock-based compensation expense 7,191 9,294 Redemption value adjustments $ 3,512 $ 3,273

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	The following is a summary of the Company’s fixed assets as of December 31: 2018 2017 Cost Accumulated Depreciation Net Book Value Cost Accumulated Depreciation Net Book Value Computers, furniture and fixtures $ 100,276 $ (73,060 ) $ 27,216 $ 101,806 $ (74,429 ) $ 27,377 Leasehold improvements 116,459 (55,486 ) 60,973 112,099 (49,170 ) 62,929 $ 216,735 $ (128,546 ) $ 88,189 $ 213,905 $ (123,599 ) $ 90,306

Noncontrolling and Redeemable_2

Noncontrolling and Redeemable Noncontrolling Interests (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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, 2018 and 2017 were as follows: Noncontrolling Interests Balance, December 31, 2016 $ 4,154 Income attributable to noncontrolling interests 15,375 Distributions made (8,865 ) Other (1) 366 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
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: Year Ended December 31, 2018 2017 2016 Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Transfers from the noncontrolling interests Increase in MDC Partners Inc. paid-in capital for purchase of equity interests in excess of noncontrolling interests and redeemable noncontrolling interests 10,140 2,315 22,776 Net transfers from noncontrolling interests $ 10,140 $ 2,315 $ 22,776 Change from net income (loss) attributable to MDC Partners Inc. and transfers (to) from noncontrolling interests $ (113,593 ) $ 244,163 $ (23,063 )
Redeemable Noncontrolling Interest [Table Text Block]	The following table presents changes in redeemable noncontrolling interests as of December 31, 2018 and 2017 : 2018 2017 Beginning Balance $ 62,886 $ 60,180 Redemptions (11,943 ) (910 ) Granted — 1,666 Changes in redemption value 1,067 1,498 Currency translation adjustments (464 ) 452 Ending balance $ 51,546 $ 62,886	s

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill Global Integrated Agencies Domestic Creative Agencies Specialist Communications Media Services All Other Total Balance at December 31, 2016 $ 350,716 $ 36,762 $ 78,691 $ 176,686 $ 201,904 $ 844,759 Acquired goodwill — — — — — Disposition (964 ) — — (16,629 ) — (17,593 ) Impairment loss recognized (2,741 ) — — (497 ) — (3,238 ) Transfer of goodwill between segments 6,371 — — 497 (6,868 ) — Foreign currency translation 5,689 218 15 — 6,085 12,007 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 (1) See Note 5 of the Notes to the Consolidated Financial Statements included herein for additional information. The Company recognized an impairment of goodwill and other assets of $80,057 for the twelve months ended December 31, 2018 . The impairment primarily consists 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. The impairment of goodwill was in connection with the Company’s interim and annual impairment tests performed in 2018. See below for information regarding an impairment of a tradename. The Company recognized an impairment of goodwill and other assets of $4,415 for the twelve months ended December 31, 2017. The impairment primarily consists 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 impairment of goodwill was in connection with the Company’s annual impairment test performed in 2017. The Company recognized an impairment of goodwill of $48,524 for the twelve months ended December 31, 2016. The impairment was recognized at three reporting units, the Specialist Communications reportable segment, Media Services reportable segment and All Other reportable segment. The impairment of goodwill was in connection with the Company’s interim and annual impairment tests performed in 2016. The total accumulated goodwill impairment charges are $173,205 through December 31, 2018 . As of December 31, the gross and net amounts of acquired intangible assets other than goodwill were as follows: For the Year Ended December 31, Intangible Assets 2018 2017 Trademarks (indefinite life) $ 14,600 $ 17,780 Customer relationships – gross $ 93,296 $ 102,325 Less accumulated amortization (59,144 ) (73,767 ) Customer relationships – net $ 34,152 $ 28,558 Other intangibles – gross $ 40,803 $ 37,273 Less accumulated amortization (21,790 ) (13,006 ) Other intangibles – net $ 19,013 $ 24,267 Total intangible assets $ 148,699 $ 157,378 Less accumulated amortization (80,934 ) (86,773 ) Total intangible assets – net $ 67,765 $ 70,605
Schedule of Intangible Assets and Goodwill	For the Year Ended December 31, Intangible Assets 2018 2017 Trademarks (indefinite life) $ 14,600 $ 17,780 Customer relationships – gross $ 93,296 $ 102,325 Less accumulated amortization (59,144 ) (73,767 ) Customer relationships – net $ 34,152 $ 28,558 Other intangibles – gross $ 40,803 $ 37,273 Less accumulated amortization (21,790 ) (13,006 ) Other intangibles – net $ 19,013 $ 24,267 Total intangible assets $ 148,699 $ 157,378 Less accumulated amortization (80,934 ) (86,773 ) Total intangible assets – net $ 67,765 $ 70,605
Finite-lived Intangible Assets Amortization Expense	The estimated amortization expense for the five succeeding years is as follows: Year Amortization 2019 $ 12,257 2020 9,601 2021 8,220 2022 7,666 2023 and thereafter 15,421

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2018
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: 2018 2017 2016 Income (Loss): U.S. $ (68,698 ) $ 48,053 $ (16,661 ) Non-U.S. (11,709 ) 39,025 (33,055 ) $ (80,407 ) $ 87,078 $ (49,716 )
Schedule Of Components Of Income Taxes Provision Benefit	The provision (benefit) for income taxes by taxing jurisdiction for the years ended December 31, were: 2018 2017 2016 Current tax provision U.S. federal $ 444 $ (1,657 ) $ — U.S. state and local 2 98 (1,520 ) Non-U.S. 7,584 6,514 2,154 8,030 4,955 634 Deferred tax provision (benefit): U.S. federal (9,315 ) (172,873 ) 5,785 U.S. state and local (2,990 ) (7,775 ) (3,550 ) Non-U.S. 35,878 7,629 (12,273 ) 23,573 (173,019 ) (10,038 ) Income tax provision (benefit) $ 31,603 $ (168,064 ) $ (9,404 )
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: 2018 2017 2016 Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest $ (80,407 ) $ 87,078 $ (49,716 ) Statutory income tax rate 21.0 % 35.0 % 35.0 % Tax expense (benefit) using statutory income tax rate (16,886 ) 30,477 (17,401 ) State and foreign taxes (2,988 ) 8,863 (94 ) Non-deductible stock-based compensation 1,512 1,441 1,123 Other non-deductible expense 10,091 (220 ) 1,848 Change to valuation allowance 49,482 (103,212 ) 6,605 Effect of the difference in U.S. federal and local statutory rates (152 ) (2,939 ) (353 ) Impact of tax reform — (100,472 ) — Noncontrolling interests (2,674 ) (4,413 ) (1,287 ) Impact of foreign operations 1,711 (2,453 ) — Adjustment to deferred tax balances (8,865 ) — — Other, net 372 4,864 155 Income tax expense (benefit) $ 31,603 $ (168,064 ) $ (9,404 ) Effective income tax rate (39.3 )% (193.0 )% 18.9 %
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: 2018 2017 Deferred tax assets: Capital assets and other $ 905 $ 5,059 Net operating loss carry forwards 70,646 49,318 Interest deductions 8,911 2,026 Refinancing charge 2,926 5,578 Goodwill and intangibles 123,504 129,455 Stock compensation 2,101 1,208 Pension plan 3,872 4,165 Unrealized foreign exchange 14,645 8,653 Capital loss carry forwards 11,827 11,450 Accounting reserves 8,280 412 Gross deferred tax asset 247,617 217,324 Less: valuation allowance (68,479 ) (19,032 ) Net deferred tax assets 179,138 198,292 Deferred tax liabilities: Goodwill amortization (91,726 ) (89,727 ) Total deferred tax liabilities (91,726 ) (89,727 ) Net deferred tax asset (liability) $ 87,412 $ 108,565 Disclosed as: Deferred tax assets $ 92,741 $ 115,325 Deferred tax liabilities (5,329 ) (6,760 ) $ 87,412 $ 108,565
Schedule Of Changes In Tax Reserve	2018 2017 2016 A reconciliation of the change in unrecognized tax benefits is as follows: Unrecognized tax benefit - Beginning Balance $ 1,433 $ 1,465 $ 3,605 Current year positions — 489 — Prior period positions 7 (436 ) (134 ) Settlements (314 ) — (1,374 ) Lapse of statute of limitations (239 ) (85 ) (632 ) Unrecognized tax benefits - Ending Balance $ 887 $ 1,433 $ 1,465

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
Schedule of Debt		As of December 31, the Company’s indebtedness was comprised as follows: 2018 2017 Revolving credit agreement $ 68,143 $ — 6.50% Notes due 2024 900,000 900,000 Debt issuance costs (14,036 ) (17,587 ) 954,107 882,413 Obligations under capital leases 478 706 954,585 883,119 Less: Current portion of long-term debt (356 ) (313 ) $ 954,229 $ 882,806
Schedule Of Future Principal Repayments Of Long Term Debt Including Capital Lease Obligations	Future principal repayments, including capital lease obligations, for the years ended December 31, and in aggregate, are as follows: Period Amount 2019 $ 356 2020 101 2021 68,164 2022 — 2023 — 2024 and thereafter 900,000 $ 968,621
Schedule of Future Minimum Lease Payments for Capital Leases	Future minimum capital lease payments for the years ended December 31 and in aggregate, are as follows: Period Amount 2019 $ 356 2020 101 2021 21 2022 — 2023 — 2024 and thereafter — 478 Less: imputed interest (42 ) 436 Less: current portion (356 ) $ 80 Capital lease obligations at December 31 were: 2018 2017 Current $ 356 $ 313 Long-term 122 393 $ 478 $ 706

Share Capital (Tables)

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Share-based Compensation, Stock Options and Stock Appreciation Rights Award Activity [Table Text Block]	SAR Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2017 327,500 $ 2.35 $ 6.60 Granted — — — Vested — — — Forfeited (76,700 ) 2.35 6.60 Exercised — — — Balance at December 31, 2018 250,800 $ 2.35 $ 6.60
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, 2017 — $ — 785,085 $ 11.94 Granted 503,321 9.17 156,440 7.38 Vested (4,444 ) 10.30 (239,085 ) 14.99 Forfeited (45,965 ) 9.29 (75,500 ) 9.75 Balance at December 31, 2018 452,912 $ 9.15 626,940 $ 9.83
Schedule of Share-based Compensation, Stock Options, Activity		share option awards: Share Option Awards Shares Weighted Average Weighted Average Exercise Price Balance at December 31, 2017 — $ — $ — Granted 111,866 2.23 4.85 Vested — — — Forfeited — — — Exercised — — — Balance at December 31, 2018 111,866 $ 2.23 $ 4.85

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2018
Fair Value, Inputs, Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Liabilities Measured on Recurring and Nonrecurring Basis	The following table presents certain information for our financial liability that is measured at fair value on a recurring basis at December 31: 2018 2017 Carrying Amount Fair Value Carrying Amount Fair Value Liabilities: 6.50% Senior Notes due 2024 $ 900,000 $ 834,750 $ 900,000 $ 904,500

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2018
Segment Reporting [Abstract]
Schedule of Segment Reporting Information, by Segment	Years Ended December 31, 2018 2017 2016 Revenue: Global Integrated Agencies $ 698,872 $ 797,347 $ 712,793 Domestic Creative Agencies 102,063 104,417 97,199 Specialist Communications 179,065 172,565 170,285 Media Services 140,753 166,216 157,696 All Other 355,450 273,234 247,812 Total $ 1,476,203 $ 1,513,779 $ 1,385,785 Segment operating income (loss): Global Integrated Agencies $ 44,868 $ 71,857 $ 59,193 Domestic Creative Agencies 18,552 19,333 18,089 Specialist Communications 18,629 20,728 1,940 Media Services (51,196 ) 13,126 5,554 All Other 34,000 47,771 7,773 Corporate (55,157 ) (40,856 ) (44,118 ) Total $ 9,696 $ 131,959 $ 48,431 Other Income (Expense): Interest expense and finance charges, net (67,075 ) (64,364 ) (65,050 ) Foreign exchange transaction gain (loss) (23,258 ) 18,137 (213 ) Loss on redemption of Notes — — (33,298 ) Other, net 230 1,346 414 Income (loss) before income taxes and equity in earnings (losses) of non-consolidated affiliates (80,407 ) 87,078 (49,716 ) Income tax expense (benefit) 31,603 (168,064 ) (9,404 ) Income (loss) before equity in earnings (losses) of non-consolidated affiliates (112,010 ) 255,142 (40,312 ) Equity in earnings (losses) of non-consolidated affiliates 62 2,081 (309 ) Net income (loss) (111,948 ) 257,223 (40,621 ) Net income attributable to the noncontrolling interest (11,785 ) (15,375 ) (5,218 ) Net income (loss) attributable to MDC Partners Inc. $ (123,733 ) $ 241,848 $ (45,839 ) Years Ended December 31, 2018 2017 2016 Depreciation and amortization: Global Integrated Agencies $ 23,571 $ 23,831 $ 21,555 Domestic Creative Agencies 1,583 1,582 1,811 Specialist Communications 4,252 4,714 6,637 Media Services 3,119 4,052 6,091 All Other 12,909 8,197 8,768 Corporate 762 1,098 1,584 Total $ 46,196 $ 43,474 $ 46,446 Stock-based compensation: Global Integrated Agencies $ 8,521 $ 15,225 $ 12,177 Domestic Creative Agencies 1,100 887 651 Specialist Communications 714 2,954 3,629 Media Services 318 656 318 All Other 3,104 2,494 1,703 Corporate 4,659 2,134 2,525 Total $ 18,416 $ 24,350 $ 21,003 Capital expenditures: Global Integrated Agencies $ 10,088 $ 20,760 $ 16,486 Domestic Creative Agencies 951 1,168 1,153 Specialist Communications 3,618 1,288 2,741 Media Services 966 3,842 5,266 All Other 4,574 5,877 3,753 Corporate 67 23 33 Total $ 20,264 $ 32,958 $ 29,432
Schedule Of Fixed Assets Goodwill Intangibles Net	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 2018 $ 76,781 $ 4,779 $ 6,629 $ 88,189 2017 $ 77,163 $ 5,638 $ 7,505 $ 90,306 Goodwill and Intangible Assets 2018 $ 679,344 $ 61,748 $ 67,628 $ 808,720 2017 $ 706,241 $ 127,014 $ 73,285 $ 906,540
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas	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: 2018 $ 1,153,192 $ 124,000 $ 199,011 $ 1,476,203 2017 $ 1,172,364 $ 123,092 $ 218,323 $ 1,513,779 2016 $ 1,103,714 $ 124,101 $ 157,970 $ 1,385,785

Commitments, Contingencies an_2

Commitments, Contingencies and Guarantees (Tables)	12 Months Ended
	Dec. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases	Minimum rental commitments for the rental of office and production premises and equipment under non-cancellable leases net of sublease income, some of which provide for rental adjustments due to increased property taxes and operating costs, for the years ending December 31, 2019 and thereafter, are as follows: Period Amount 2019 $ 58,015 2020 55,211 2021 45,974 2022 40,387 2023 38,348 2024 and thereafter 107,975 $ 345,910

New Accounting Pronouncements N

New Accounting Pronouncements New Accounting Pronouncements (Tables)	12 Months Ended
	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of Change in Accounting Estimate [Table Text Block]	The following table summarizes the impact of adoption of ASC 606 on the Consolidated Statement of Operations during the twelve months ended December 31, 2018 : Twelve Months Ended December 31, 2018 As Reported Adjustments Adjusted to Exclude Adoption of ASC 606 Revenue - Services $ 1,476,203 $ 51,636 $ 1,527,839 Costs of services sold $ 991,198 $ 62,358 $ 1,053,556 Operating income (loss) $ 9,696 $ (10,722 ) $ (1,026 ) Net loss attributable to MDC Partners Inc. common shareholders $ (132,088 ) $ (6,883 ) $ (138,971 ) Loss per common share - basic and diluted $ (2.31 ) $ (0.12 ) $ (2.43 )

Employee Benefit Plans (Tables)

Employee Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
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 Pension Pension 2018 2017 2016 Service cost $ — $ — $ — Interest cost on benefit obligation 1,641 1,725 1,855 Expected return on plan assets (1,948 ) (1,830 ) (1,863 ) Curtailment and settlements 1,039 — 929 Amortization of actuarial losses 258 222 137 Net periodic benefit cost $ 990 $ 117 $ 1,058
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 Pension 2018 2017 Current year actuarial (gain) loss $ (520 ) $ 1,558 Amortization of actuarial loss (258 ) (222 ) Total recognized in other comprehensive (income) loss $ (778 ) $ 1,336 Total recognized in net periodic benefit cost and other comprehensive (income) loss $ 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: 2018 2017 Change in benefit obligation: Benefit obligation, Beginning balance $ 43,750 $ 40,722 Interest Cost 1,641 1,725 Actuarial losses (3,522 ) 3,088 Benefits paid (3,931 ) (1,785 ) Benefit obligation, Ending balance 37,938 43,750 Change in plan assets: Fair value of plan assets, Beginning balance 27,977 24,482 Actual return on plan assets (2,093 ) 3,360 Employer contributions 1,228 1,920 Benefits paid (3,931 ) (1,785 ) Fair value of plan assets, Ending balance 23,181 27,977 Unfunded status $ 14,757 $ 15,773
Schedule of Amounts Recognized in Balance Sheet		Pension Pension 2018 2017 Non-current liability $ 14,757 $ 15,773 Net amount recognized $ 14,757 $ 15,773
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 Pension 2018 2017 Accumulated net actuarial losses $ 12,878 $ 13,656 Amount recognized $ 12,878 $ 13,656
Schedule Of Assumptions Used To Determine Benefit Obligations	eighted average assumptions were used to determine benefit obligations as of December 31: Pension Pension 2018 2017 Discount rate 4.42 % 3.83 % Rate of compensation increase N/A N/A
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 Pension Pension 2018 2017 2016 Discount rate 3.83 % 4.32 % 4.69 % Expected return on plan assets 7.00 % 7.40 % 7.40 % Rate of compensation increase N/A 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, 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 $ — $ — December 31, 2017 Level 1 Level 2 Level 3 Asset Category: Money Market Fund – Short Term Investments $ 1,695 $ 1,695 $ — $ — Mutual Funds 26,282 26,282 — — Total $ 27,977 $ 27,977 $ — $ —
Schedule of Allocation of Plan Assets	The pension plans weighted-average asset allocation for the years ended December 31, 2018 , and 2017 are as follows: Target Allocation Actual Allocation Actual Allocation 2018 2018 2017 Asset Category: Equity Securities 65.0 % 67.0 % 68.9 % Debt Securities 30.0 % 25.5 % 25.0 % Cash/Cash Equivalents and Short Term Investments 5.0 % 7.5 % 6.1 % 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 2019 $ 1,690 2020 1,857 2021 1,848 2022 1,912 2023 2,139 2024 – 2027 11,047

Changes in Accumulated Other _2

Changes in Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2018
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, 2016 $ (12,320 ) $ 10,496 $ (1,824 ) Other comprehensive income before reclassifications — 1,206 1,206 Amounts reclassified from accumulated other comprehensive income (loss) (1,336 ) — (1,336 ) Other comprehensive income (loss) (1,336 ) 1,206 (130 ) 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 (loss) (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

Quarterly Results of Operatio_2

Quarterly Results of Operations (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of Quarterly Financial Information	. 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: 2018 $ 326,968 $ 379,743 $ 375,830 $ 393,662 2017 $ 344,700 $ 390,532 $ 375,800 $ 402,747 Cost of services sold: 2018 $ 243,030 $ 253,390 $ 238,690 $ 256,088 2017 $ 237,563 $ 267,822 $ 249,418 $ 268,673 Net Income (loss): 2018 $ (28,519 ) $ 5,951 $ (13,667 ) $ (75,713 ) 2017 $ (9,683 ) $ 13,467 $ 21,984 $ 231,455 Net income (loss) attributable to MDC Partners Inc.: 2018 $ (29,416 ) $ 3,406 $ (16,125 ) $ (81,598 ) 2017 $ (10,566 ) $ 11,253 $ 18,493 $ 222,668 Income (loss) per common share: Basic 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) 2017 $ (0.21 ) $ 0.14 $ 0.25 $ 3.33 Diluted 2018 $ (0.56 ) $ 0.02 $ (0.32 ) $ (1.46 ) 2017 $ (0.21 ) $ 0.14 $ 0.24 $ 3.30

Basis of Presentation Basis of

Basis of Presentation Basis of Presentation (Details) $ / shares in Units, $ in Millions	Mar. 14, 2019USD ($)$ / sharesshares	Mar. 08, 2019USD ($)	Dec. 31, 2018reportable_segment
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment			4
Common Class A | Subsequent Event [Member]
Segment Reporting Information [Line Items]
Price per share | $ / shares	$ 3.50
Kingsdale Partners, LP | Subsequent Event [Member]
Segment Reporting Information [Line Items]
Proceeds from sale of business		$ 50
Common Stock | Common Class A | Subsequent Event [Member]
Segment Reporting Information [Line Items]
Class A shares issued | shares	14,285,714
Proceeds from sale of Class A shares	$ 50
Convertible Preference Shares | Series 6 Convertible Preferred Shares [Member] | Subsequent Event [Member]
Segment Reporting Information [Line Items]
Series 6 convertible preference shares issued | shares	50,000
Proceeds from issuance of Series 6 convertible preference shares	$ 50

Significant Accounting Polici_4

Significant Accounting Policies - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2016
Redeemable Noncontrolling Interest [Line Items]
Consolidated Accounts Receivable Percentage	10.00%	10.00%
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests	$ (25,550)	$ (8,936)
Redeemable Noncontrolling Interest, Equity, Redemption Value	62,886
Noncontrolling Interest, Change in Redemption Value	(5,965)
Redeemable Noncontrolling Interest, Equity, Redemption Value	$ 51,546

Significant Accounting Polici_5

Significant Accounting Policies - Textual (Details)	Oct. 01, 2017	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)Clientsshares	Dec. 31, 2018USD ($)reportable_segment	Dec. 31, 2017USD ($)Clientsreportable_segmentshares	Dec. 31, 2016USD ($)Clientsreportable_segment$ / sharesshares	Dec. 31, 2015Clients$ / sharesshares	May 03, 2016USD ($)	Mar. 23, 2016	Dec. 31, 2014	Dec. 31, 2013	Mar. 20, 2013
Significant Accounting Policies [Line Items]
Cash held in trusts		$ 0	$ 4,632,000	$ 0	$ 4,632,000
Accretion on Convertible Preferred Shares				(8,355,000)	6,352,000	$ 0
Earnings Per Share, Increase (Decrease) Due To Non-Controlling Dividend As A Result Of Redeemable Redemption Value In Excess of Fair Value | $ / shares						$ 0	$ 0
Long-Term Growth Rate Assumed in Annual Goodwill Impairment Test	3.00%
Debt Issuance Costs, Net		$ 14,036,000	$ 17,587,000	14,036,000	17,587,000
Income attributable to fair value adjustments				$ (374,000)	$ (4,819,000)	$ 8,227,000
Clients exceeding consolidated accounts receivable percentage | Clients			0		0	0
Number of Reporting Units | reportable_segment				3	2	3
Consolidated accounts receivable percentage		10.00%		10.00%		10.00%
Clients exceeding consolidated largest client revenue | Clients						0	0
Consolidated largest client revenue				10.00%		10.00%	10.00%
Distributions from non-consolidated affiliates				$ 963,000	$ 3,672,000	$ 7,402,000
Cost method investments		$ 8,072,000	$ 9,527,000	8,072,000	9,527,000
Goodwill, Impairment Loss				74,560,000	3,238,000
Assets		1,611,573,000	1,698,892,000	1,611,573,000	1,698,892,000
Liabilities		$ 1,806,994,000	1,791,519,000	1,806,994,000	1,791,519,000
Stock Issued During Period, Shares, New Issues | shares						0	0
Stock-based compensation				5,892,000	5,335,000	$ 5,808,000
Pension expense				$ 9,810,000	$ 10,124,000	10,026,000
Stock Appreciation Rights (SARs)
Significant Accounting Policies [Line Items]
Risk free interest rate				1.70%
Expected volatility rate				46.20%
Expected term				4 years
Minimum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					3 years
Weighted Average Cost Of Capital, Annual Goodwill Impairment Test	9.67%
Maximum
Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life					7 years
Equity method investment, ownership percentage		50.00%		50.00%
Weighted Average Cost Of Capital, Annual Goodwill Impairment Test	11.85%
Contingent Payment [Member]
Significant Accounting Policies [Line Items]
Income attributable to fair value adjustments		$ 8,979,000	$ 18,173,000	$ (3,679,000)	$ (6,021,000)
Six Point Five Zero Percentage Notes [Domain]
Significant Accounting Policies [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		6.50%		6.50%					6.50%
Six Point Seven Five Percentage Notes [Member]
Significant Accounting Policies [Line Items]
Debt Instrument, Interest Rate, Stated Percentage										6.75%	6.75%	6.75%
Interest Expense [Member] | Fixed Payment [Member]
Significant Accounting Policies [Line Items]
Income attributable to fair value adjustments				$ 87,000	100,000	$ 255,000
Quantitative Assessment [Member]
Significant Accounting Policies [Line Items]
Number of Reporting Units						13
Specialist Communications [Member]
Significant Accounting Policies [Line Items]
Goodwill, Impairment Loss				0	0
All Other [Domain]
Significant Accounting Policies [Line Items]
Goodwill, Impairment Loss				4,691,000	0
Domestic Creative Agencies [Member]
Significant Accounting Policies [Line Items]
Goodwill, Impairment Loss				0	0
Wells Fargo Capital Finance, Llc [Member] | Revolving Credit Facility [Member]
Significant Accounting Policies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity								$ 325,000,000
Assets and liabilities held for sale
Significant Accounting Policies [Line Items]
Cash held in trusts		$ 4,000		4,000
Convertible Preference Shares | Convertible preference shares
Significant Accounting Policies [Line Items]
Accretion on Convertible Preferred Shares				$ (8,355,000)	$ (36,254,000)
Shares authorized | shares			95,000		95,000
Shares issued | shares			95,000		95,000

Revenue (Details)

Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue [Abstract]
Revenue performance obligation	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.
Customer Advances, Current	$ 138,505	$ 148,133
Unbilled Contracts Receivable	64,362	54,177
Expenditures Billable Current	$ 42,369	$ 31,146

Revenue Disaggregation of Reven

Revenue Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Services	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 402,747	$ 375,800	$ 390,532	$ 344,700	$ 1,476,203	$ 1,513,779	$ 1,385,785
United States
Disaggregation of Revenue [Line Items]
Services									1,153,192	1,172,364	1,103,714
Canada
Disaggregation of Revenue [Line Items]
Services									124,000	123,092	124,101
Other Geographical Location [Member]
Disaggregation of Revenue [Line Items]
Services									199,011	218,323	157,970
Food & Beverage [Member]
Disaggregation of Revenue [Line Items]
Services									313,368	313,786	266,600
Retail [Member]
Disaggregation of Revenue [Line Items]
Services									152,552	178,152	182,428
Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Services									162,524	162,307	147,849
Communications [Member]
Disaggregation of Revenue [Line Items]
Services									178,410	208,701	160,064
Automotive [Member]
Disaggregation of Revenue [Line Items]
Services									88,807	127,023	129,352
Technology [Member]
Disaggregation of Revenue [Line Items]
Services									104,479	99,325	109,309
Health Care [Member]
Disaggregation of Revenue [Line Items]
Services									127,547	124,261	115,159
Financials [Member]
Disaggregation of Revenue [Line Items]
Services									110,069	104,713	85,480
Transportation and Travel/Lodging [Member]
Disaggregation of Revenue [Line Items]
Services									86,419	56,955	58,298
Other [Member]
Disaggregation of Revenue [Line Items]
Services									152,028	$ 138,556	$ 131,246
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member]
Disaggregation of Revenue [Line Items]
Services									51,636
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | United States
Disaggregation of Revenue [Line Items]
Services									20,699
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Canada
Disaggregation of Revenue [Line Items]
Services									(1,288)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Other Geographical Location [Member]
Disaggregation of Revenue [Line Items]
Services									32,225
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Food & Beverage [Member]
Disaggregation of Revenue [Line Items]
Services									7,064
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Retail [Member]
Disaggregation of Revenue [Line Items]
Services									(2,683)
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Services									585
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Services									25,957
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Services									8,587
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Technology [Member]
Disaggregation of Revenue [Line Items]
Services									38
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Health Care [Member]
Disaggregation of Revenue [Line Items]
Services									507
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Financials [Member]
Disaggregation of Revenue [Line Items]
Services									146
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Transportation and Travel/Lodging [Member]
Disaggregation of Revenue [Line Items]
Services									2,461
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Accounting Standards Update 2014-09 [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Services									8,974
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Disaggregation of Revenue [Line Items]
Services									1,527,839
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | United States
Disaggregation of Revenue [Line Items]
Services									1,173,891
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Canada
Disaggregation of Revenue [Line Items]
Services									122,712
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other Geographical Location [Member]
Disaggregation of Revenue [Line Items]
Services									231,236
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Food & Beverage [Member]
Disaggregation of Revenue [Line Items]
Services									320,432
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Retail [Member]
Disaggregation of Revenue [Line Items]
Services									149,869
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Consumer Products [Member]
Disaggregation of Revenue [Line Items]
Services									163,109
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Communications [Member]
Disaggregation of Revenue [Line Items]
Services									204,367
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Automotive [Member]
Disaggregation of Revenue [Line Items]
Services									97,394
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Technology [Member]
Disaggregation of Revenue [Line Items]
Services									104,517
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Health Care [Member]
Disaggregation of Revenue [Line Items]
Services									128,054
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Financials [Member]
Disaggregation of Revenue [Line Items]
Services									110,215
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Transportation and Travel/Lodging [Member]
Disaggregation of Revenue [Line Items]
Services									88,880
Calculated under Revenue Guidance in Effect before Topic 606 [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Services									$ 161,002

Revenue Contract Assets and Lia

Revenue Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Customer Advances, Current	$ 138,505	$ 148,133
Deferred Revenue, Additions	9,628
Unbilled Contracts Receivable	64,362	$ 54,177
Deferred Revenue, Revenue Recognized	$ 135,573

Loss per Common Share - Schedu

Loss per Common Share - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Net income attributable to MDC Partners	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ 222,668	$ 18,493	$ 11,253	$ (10,566)	$ (123,733)	$ 241,848	$ (45,839)
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	$ (75,713)	$ (13,667)	$ 5,951	$ (28,519)	$ 231,455	$ 21,984	$ 13,467	$ (9,683)	(111,948)	257,223	(40,621)
Accretion on Convertible Preferred Shares									(8,355)	6,352	0
Net Income Allocated to Convertible Shares									0		0
Income (Loss) from Continuing Operations Attributable to Parent, Basic									(132,088)	205,594	(45,839)
Numerator:
Net income attributable to the noncontrolling interests									(11,785)	(15,375)	(5,218)
Income (Loss) from Continuing Operations Attributable to Parent											(45,839)
Adjustment to Net Income, Allocated to Convertible Shares									0	106	0
Income (Loss) from Continuing Operations Attributable to Parent, Diluted									$ (132,088)	$ 205,700	$ (45,839)
Denominator:
Basic weighted average number of common shares outstanding									57,218,994	55,255,797	51,345,807
Effect of dilutive securities:
Impact of stock options and non-vested stock under employee stock incentive plans									0	225,989	0
Diluted weighted average number of common shares outstanding									57,218,994	55,481,786	51,345,807
Income (Loss) from Continuing Operations, Per Basic Share									$ (2.31)	$ 3.72	$ (0.89)
Income (Loss) from Continuing Operations, Per Diluted Share									$ (2.31)	$ 3.71	$ (0.89)
Series 4 Convertible Preferred Stock [Member] | Convertible Preference Shares
Class of Stock [Line Items]
Accretion on Convertible Preferred Shares										$ (6,352)
Convertible preference shares | Convertible Preference Shares
Class of Stock [Line Items]
Accretion on Convertible Preferred Shares									$ (8,355)	(36,254)
Net Income Allocated to Convertible Shares										$ (29,902)

Loss per Common Share - Textua

Loss per Common Share - Textual (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accretion on Convertible Preferred Shares	$ (8,355)	$ 6,352	$ 0
Income (Loss) from Continuing Operations, Per Basic Share	$ (2.31)	$ 3.72	$ (0.89)
Net Income Allocated to Convertible Shares	$ 0		$ 0
Antidilutive securities excluded from computation of earnings per share, amount	1,442,518	0	1,391,456
Contingent Restricted Stock Units (RSUs) [Member]
Antidilutive securities excluded from computation of earnings per share, amount	1,012,637	1,443,921	503,321
Convertible Preference Shares | Series 4 Convertible Preferred Stock [Member]
Accretion on Convertible Preferred Shares		$ (6,352)
Shares, Outstanding	95,000,000	95,000,000
Convertible Preferred Stock, Shares Issued upon Conversion	10,970,714	10,135,244

Acquisitions - Textual (Detail

Acquisitions - Textual (Details) - USD ($)	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Income attributable to fair value adjustments				$ (374,000)	$ (4,819,000)	$ 8,227,000
Share-based Compensation		$ 1,534,000	$ 7,480,000	18,416,000	24,350,000	21,003,000
Goodwill, Written off Related to Sale of Business Unit					17,593,000
Goodwill				37,592,000	0
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests				$ (25,550,000)		(8,936,000)
Intangible assets amortization period (years)				7 years
Stock-based compensation expense				$ 7,191,000	9,294,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings				3,512,000	3,273,000
Stock Issued During Period, Value, Acquisitions						34,219,000
Business Combination, Contingent Consideration, Liability		83,695,000	122,426,000	83,695,000	122,426,000
Noncontrolling Interest, Increase from Business Combination				0	1,666,000
Asset Impairment Charges		56,732,000		80,057,000	4,415,000	48,524,000
Goodwill		740,955,000	835,935,000	740,955,000	835,935,000	$ 844,759,000
Aggregate 2018 Step-up Transaction [Member] [Member]
Business Acquisition [Line Items]
Cost of acquired entity, cash paid				3,000
Deferred acquisition consideration		$ 4,305		4,305
Allison & Partners LLC [Member]
Business Acquisition [Line Items]
Percentage of voting interests acquired	24.50%
Business Combination, Consideration Transferred				10,000
Cost of acquired entity, cash paid				0
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination	$ 20,096
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests				9,000
Business Combination, Contingent Consideration, Liability	$ 10,000
Noncontrolling Interest, Increase from Business Combination				$ 1,000
Aggregate 2017 Step Up Transactions [Domain]
Business Acquisition [Line Items]
Share-based Compensation					996
Cost of acquired entity, cash paid					3,858
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests					11,965
Business Combination, Contingent Consideration, Liability			7,208		7,208
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value					816
Noncontrolling Interest, Period Increase (Decrease)					397
Noncontrolling Interest, Increase from Business Combination					2,315
Aggregate 2017 Dispositions [Domain]
Business Acquisition [Line Items]
Share-based Compensation					2,000
Goodwill, Written off Related to Sale of Business Unit					17,593
Noncontrolling Interest, Decrease from Deconsolidation					10,657,000
OneChocolate [Domain]
Business Acquisition [Line Items]
Percentage of voting interests acquired		100.00%		100.00%
Business Combination, Consideration Transferred				$ 3,231
Deferred acquisition consideration		$ 2,146		2,146
Working capital payments		$ 966		$ 966
Instrument [Domain]
Business Acquisition [Line Items]
Percentage of voting interests acquired		51.00%		51.00%
Business Combination, Consideration Transferred				$ 35,591
Cost of acquired entity, cash paid				29,000
Noncontrolling Interest, Increase from Business Combination				27,357
Business Combination, Consideration Transferred, Other				10,304
Finite-lived Intangible Assets Acquired				23,130
Goodwill		$ 32,776		$ 32,776
Doner [Domain]
Business Acquisition [Line Items]
Percentage of voting interests acquired		14.90%		14.90%
Business Combination, Consideration Transferred, Including Equity Interest in Acquiree Held Prior to Combination				$ 16,361
Kingsdale Partners, LP
Business Acquisition [Line Items]
Asset Impairment Charges				$ 5,000
Source [Domain]
Business Acquisition [Line Items]
Percentage of voting interests acquired		3.00%		3.00%
Doner and Source [Domain]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred				$ 7,618
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests				12,000
Business Combination, Acquisition of Less than 100 Percent, Redeemable Noncontrolling Interest, Fair Value				$ 1,000
Noncontrolling Interest Equity [Domain] | Aggregate 2017 Dispositions [Domain]
Business Acquisition [Line Items]
Noncontrolling Interest, Increase from Sale of Parent Equity Interest					$ 6,961
Common Stock
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions				108,898	(161,535)	1,900,000
Redeemable Noncontrolling Interest [Member] | Aggregate 2017 Dispositions [Domain]
Business Acquisition [Line Items]
Redeemable Noncontrolling Interest, Increase from Sale of Equity Interest					$ 1,690
Additional Paid-in Capital
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests				$ (10,140,000)	(2,315,000)	$ (22,776,000)
Stock Issued During Period, Value, Acquisitions				7,030,000		34,219,000
Noncontrolling Interest, Increase from Business Combination					(5,654,000)
Noncontrolling Interest [Member]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests				(15,410,000)	11,965,000	13,840,000
Noncontrolling Interest, Increase from Business Combination					12,614,000
Noncontrolling Interest [Member] | Aggregate 2017 Dispositions [Domain]
Business Acquisition [Line Items]
Noncontrolling Interest, Decrease from Deconsolidation					10,657,000
Contingent Payment [Member]
Business Acquisition [Line Items]
Income attributable to fair value adjustments		$ 8,979,000	18,173,000	(3,679,000)	(6,021,000)
Fixed payments [Member]
Business Acquisition [Line Items]
Business Combination, Contingent Consideration, Liability		$ 1,097,000	$ 3,340,000	$ 1,097,000	3,340,000
Common Class A | Common Stock | Instrument [Domain]
Business Acquisition [Line Items]
Stock Issued During Period, Shares, Acquisitions				1,011,561
Stock Issued During Period, Value, Acquisitions				$ 7,030
Common Class A | Common Stock | Forsman & Bodenfors AB [Domain]
Business Acquisition [Line Items]
Stock Issued During Period, Value, Acquisitions				7,030,000	$ 0	$ 34,219,000
Three subsidiaries
Business Acquisition [Line Items]
Disposal Group, Not Discontinued Operation, Gain (Loss) on Disposal				$ 1,732,000

Deferred Acquisition Consider_3

Deferred Acquisition Considerations (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			$ 119,086,000	$ 224,754,000
Payments			(54,947,000)	(110,234,000)
Additions - acquisition and step-up transactions			14,943,000	0
Redemption value adjustments			3,512,000	3,273,000
Foreign translation adjustment			4,000	1,293,000
Ending balance of contingent payments	$ 82,598,000	$ 119,086,000	82,598,000	119,086,000	$ 224,754,000
Fixed payments	83,695,000	122,426,000	83,695,000	122,426,000
Income attributable to fair value adjustments			(374,000)	(4,819,000)	8,227,000
Stock-based compensation expense			7,191,000	9,294,000
Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments				3,353,939
Contingent Payment [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Income attributable to fair value adjustments	8,979,000	18,173,000	(3,679,000)	(6,021,000)
Fixed payments [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Payments			6,000
Fixed payments	$ 1,097,000	$ 3,340,000	1,097,000	3,340,000
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments			$ 0
Common Stock | Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Redemption value adjustments				$ 28,727,000	$ 10,458,000

Fixed Assets - Schedule of Pro

Fixed Assets - Schedule of Property, Plant, and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Cost	$ 216,735	$ 213,905
Accumulated Depreciation	(128,546)	(123,599)
Net Book Value	88,189	90,306
Computers, furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Cost	100,276	101,806
Accumulated Depreciation	(73,060)	(74,429)
Net Book Value	27,216	27,377
Leasehold Improvements
Property, Plant and Equipment [Line Items]
Cost	116,459	112,099
Accumulated Depreciation	(55,486)	(49,170)
Net Book Value	$ 60,973	$ 62,929

Noncontrolling and Redeemable_3

Noncontrolling and Redeemable Noncontrolling Interests - Change in Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities and Other Liabilities [Roll Forward]
Beginning balance	$ 11,030	$ 4,154
Income attributable to noncontrolling interests	11,785	15,375	$ 5,218
Distributions to noncontrolling interests	(13,419)	(8,865)	(7,772)
Other	(118)	366
Ending balance	$ 9,278	$ 11,030	$ 4,154

Fixed Assets - Textual (Detail

Fixed Assets - Textual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation	$ 27,111	$ 23,873	$ 22,293
Capital Lease Obligations
Property, Plant and Equipment [Line Items]
Capital leased assets, gross	1,447	1,903
Capital leases, lessee balance sheet, assets by major class, accumulated depreciation	$ 780	$ 1,176

Noncontrolling and Redeemable_4

Noncontrolling and Redeemable Noncontrolling Interests - Noncontrolling Interest (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Net income (loss) attributable to MDC Partners Inc.	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ 222,668	$ 18,493	$ 11,253	$ (10,566)	$ (123,733)	$ 241,848	$ (45,839)
Transfers (to) from the noncontrolling interests
Change from net income (loss) attributable to MDC Partners Inc. and transfers (to) from noncontrolling interests									(113,593)	244,163	(23,063)
Parent [Member]
Noncontrolling Interest [Line Items]
Net income (loss) attributable to MDC Partners Inc.									(123,733)	241,848	(45,839)
Transfers (to) from the noncontrolling interests
Adjustments to Additional Paid in Capital, Changes due to Business Combinations									10,140	2,315	22,776
Net Income Loss Including Transfer from Non Controlling Interests									$ (10,140)	$ (2,315)	$ (22,776)

Noncontrolling and Redeemable_5

Noncontrolling and Redeemable Noncontrolling Interests - Redeemable Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Redeemable Noncontrolling Interest [Roll Forward]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 62,886	$ 60,180
Redeemable noncontrolling interest, redemptions, value	(11,943)	(910)
Increase in noncontrolling interests from business acquisitions	0	1,666
Redeemable noncontrolling interest, changes in redemption value	1,067	1,498
Currency translation adjustments	(464)	452
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 51,546	$ 62,886

Noncontrolling and Redeemable_6

Noncontrolling and Redeemable Noncontrolling Interests - Textual (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 51,546,000	$ 62,886,000	$ 60,180,000
Vesting over period [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	17,373,000
Termination, disability, or death [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	31,567,000
Acquisition Value in excess of Redemption Value [Member]
Noncontrolling Interest [Line Items]
Redeemable Noncontrolling Interest, Equity, Fair Value	$ 2,606,000

Accrued and Other Liabilities

Accrued and Other Liabilities - Textual (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities and Other Liabilities [Abstract]
Outstanding Checks	$ 40,271	$ 41,989
Trust liability	0	4,632
Accrued and Other Liabilities Attributable To Noncontrolling Interest	$ 9,278	$ 11,030	$ 4,154

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Schedule of Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Goodwill [Roll Forward]
Beginning Balance	$ 835,935	$ 844,759
Acquired goodwill	37,592	0
Disposition		(17,593)
Impairment loss recognized	(74,560)	(3,238)
Transfer of goodwill between segments	0	0
Transfer of goodwill to asset held for sale	(45,224)
Foreign currency translation	(12,788)	12,007
Ending Balance	740,955	835,935
Media Services [Member]
Goodwill [Roll Forward]
Beginning Balance	160,057	176,686
Acquired goodwill	0	0
Disposition		16,629
Impairment loss recognized	(52,041)	(497)
Transfer of goodwill between segments	3,773	497
Transfer of goodwill to asset held for sale	0
Foreign currency translation	(443)	0
Ending Balance	111,346	160,057
All Other [Domain]
Goodwill [Roll Forward]
Beginning Balance	201,121	201,904
Acquired goodwill	32,776
Disposition		0
Impairment loss recognized	(4,691)	0
Transfer of goodwill between segments	(22,920)	(6,868)
Transfer of goodwill to asset held for sale	(45,224)
Foreign currency translation	(6,891)	6,085
Ending Balance	154,171	201,121
Global Integrated Agencies [Member]
Goodwill [Roll Forward]
Beginning Balance	359,071	350,716
Acquired goodwill	0	0
Disposition		964
Impairment loss recognized	(17,828)	(2,741)
Transfer of goodwill between segments	17,081	6,371
Transfer of goodwill to asset held for sale	0
Foreign currency translation	(5,169)	5,689
Ending Balance	353,155	359,071
Domestic Creative Agencies [Member]
Goodwill [Roll Forward]
Beginning Balance	36,980	36,762
Acquired goodwill	0	0
Disposition		0
Impairment loss recognized	0	0
Transfer of goodwill between segments	2,066	0
Transfer of goodwill to asset held for sale	0
Foreign currency translation	(266)	218
Ending Balance	38,780	36,980
Specialist Communications [Member]
Goodwill [Roll Forward]
Beginning Balance	78,706	78,691
Acquired goodwill	4,816	0
Disposition		0
Impairment loss recognized	0	0
Transfer of goodwill between segments	0	0
Transfer of goodwill to asset held for sale	0
Foreign currency translation	(19)	15
Ending Balance	$ 83,503	$ 78,706

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Intangibles:
Trademarks (indefinite life)	$ 14,600	$ 17,780
Intangible assets, gross	148,699	157,378
Less accumulated amortization	(80,934)	(86,773)
Total intangible assets-net	67,765	70,605
Other Intangible Assets
Intangibles:
Intangible assets, gross	40,803	37,273
Less accumulated amortization	(21,790)	(13,006)
Intangible assets, net	19,013	24,267
Customer Relationships
Intangibles:
Intangible assets, gross	93,296	102,325
Less accumulated amortization	(59,144)	(73,767)
Intangible assets, net	$ 34,152	$ 28,558

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Textual (Details)	3 Months Ended	12 Months Ended
	Dec. 31, 2018USD ($)	Dec. 31, 2018USD ($)reportable_segment	Dec. 31, 2017USD ($)reportable_segment	Dec. 31, 2016USD ($)reportable_segment
Goodwill [Line Items]
Asset Impairment Charges	$ 56,732,000	$ 80,057,000	$ 4,415,000	$ 48,524,000
Number of Reporting Units | reportable_segment		3	2	3
Goodwill, impaired, accumulated impairment loss	$ 173,205,000	$ 173,205,000
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		7 years
Amortization of intangibles		$ 19,085,000	$ 19,601,000	$ 24,153,000
Amortization Of Intangible Assets, Finite Lived			$ 17,125,000	$ 21,726,000
Trademarks [Member]
Goodwill [Line Items]
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		$ 3,180,000
Customer Relationships
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		6 years
Other Intangible Assets
Goodwill [Line Items]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life		8 years
Global Integrated Agencies [Member]
Goodwill [Line Items]
Number of Reporting Units | reportable_segment		1	1
Media Services [Member]
Goodwill [Line Items]
Number of Reporting Units | reportable_segment		1	1
All Other [Member]
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]
2015	$ 12,257
2016	9,601
2017	8,220
2018	7,666
2019	$ 15,421

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Loss from continuing operations before income taxes, equity in affiliates	$ (80,407)	$ 87,078	$ (49,716)
Domestic Tax Authority
Income Tax [Line Items]
Loss from continuing operations before income taxes, equity in affiliates	(68,698)	48,053	(16,661)
Foreign Tax Authority
Income Tax [Line Items]
Loss from continuing operations before income taxes, equity in affiliates	$ (11,709)	$ 39,025	$ (33,055)

Income Taxes - Schedule of Com

Income Taxes - Schedule of Components of Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Current tax provision	$ 8,030	$ 4,955	$ 634
Deferred tax provision (benefit):	23,573	(173,019)	(10,038)
Income tax provision (benefit)	31,603	(168,064)	(9,404)
United States Federal
Income Tax [Line Items]
Current tax provision	444	(1,657)	0
Deferred tax provision (benefit):	(9,315)	(172,873)	5,785
United States And Local
Income Tax [Line Items]
Current tax provision	2	98	(1,520)
Deferred tax provision (benefit):	(2,990)	(7,775)	(3,550)
Foreign
Income Tax [Line Items]
Current tax provision	7,584	6,514	2,154
Deferred tax provision (benefit):	$ 35,878	$ 7,629	$ (12,273)

Income Taxes - Schedule of Eff

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest	$ (80,407)	$ 87,078	$ (49,716)
Statutory income tax rate	21.00%	35.00%	35.00%
Tax expense (benefit) using statutory income tax rate	$ (16,886)	$ 30,477	$ (17,401)
State and foreign taxes	(2,988)	8,863	(94)
Non-deductible stock-based compensation	1,512	1,441	1,123
Other non-deductible expense	10,091	(220)	1,848
Change to valuation allowance	49,482	(103,212)	6,605
Impact of tax reform	(152)	(2,939)	(353)
Impact of tax reform	0	(100,472)	0
Noncontrolling interests	(2,674)	(4,413)	(1,287)
Impact of foreign operations	1,711	(2,453)	0
Adjustment to deferred tax balances	(8,865)	0	0
Other, net	372	4,864	155
Income tax provision (benefit)	$ 31,603	$ (168,064)	$ (9,404)
Effective income tax rate	(39.30%)	(193.00%)	18.90%

Income Taxes - Schedule of Def

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Capital assets and other	$ 905	$ 5,059
Net operating loss carry forwards	70,646	49,318
Interest deductions	8,911	2,026
Refinancing charge	2,926	5,578
Goodwill and intangibles	123,504	129,455
Stock compensation	2,101	1,208
Pension plan	3,872	4,165
Deferred Tax Assets, Unrealized Currency Losses	14,645	8,653
Capital loss carry forwards	11,827	11,450
Accounting reserves	8,280	412
Gross deferred tax asset	247,617	217,324
Less: valuation allowance	(68,479)	(19,032)
Net deferred tax assets	179,138	198,292
Deferred tax liabilities:
Goodwill amortization	(91,726)	(89,727)
Total deferred tax liabilities	(91,726)	(89,727)
Deferred Tax Assets, Net	87,412	108,565
Disclosed as:
Deferred Tax Assets, Net of Valuation Allowance, Noncurrent	92,741	115,325
Net Deferred Tax Asset, Gross of Jurisdictional Netting		115,325
Deferred Tax Liabilities, Net, Noncurrent	$ 5,329	6,760
Deferred Tax Liability, Gross of Jurisdictional Netting		$ 6,760

Income Taxes - Schedule of Cha

Income Taxes - Schedule of Changes in Tax Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Reserve [Roll Forward]
Beginning Balance	$ 1,433	$ 1,465	$ 3,605
Current year positions	0	489	0
Prior period positions	7	(436)	(134)
Settlements	(314)	0	(1,374)
Lapse of statute of limitations	(239)	(85)	(632)
Ending Balance	$ 887	$ 1,433	$ 1,465

Income Taxes - Textual (Detail

Income Taxes - Textual (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax [Line Items]
Tax Cuts and Jobs Act of 2017, Change in Tax Rate, Deferred Tax Asset, Income Tax Expense (Benefit)				$ 26,674,000
Income tax expense (benefit)			$ 31,603,000	(168,064,000)	$ (9,404,000)
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest			(80,407,000)	87,078,000	(49,716,000)
Tax Cuts and Jobs Act of 2017, Income Tax Expense (Benefit)			$ 0	$ 100,472,000	$ 0
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent			21.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other, Amount			$ 10,091,000	$ (220,000)	$ 1,848,000
Non-deductible stock-based compensation			1,512,000	1,441,000	1,123,000
Change to valuation allowance			49,482,000	(103,212,000)	6,605,000
Impact of tax reform			(152,000)	(2,939,000)	(353,000)
Income taxes receivable	$ 4,388,000	$ 4,582,000	4,388,000	4,582,000
Taxes payable	10,045,000	3,810,000	10,045,000	3,810,000
Deferred Tax Assets, Valuation Allowance	68,479,000	19,032,000	68,479,000	$ 19,032,000
Operating loss carryforwards expiration period				2017 through 2032
Indefinite loss carryforwards	122,830,000		122,830,000
Valuation allowance, deferred tax asset, increase (decrease), amount	(49,447,000)	(226,466,000)
Unrecognized tax benefits	973,000	1,556,000	973,000	$ 1,556,000
Unrecognized tax benefits, income tax penalties and interest accrued	87,000	$ 123,000	87,000	123,000
United States Federal [Member]
Income Tax [Line Items]
Operating loss carryforwards	68,325,000		68,325,000
United States
Income Tax [Line Items]
Indefinite loss carryforwards	33,572,000		33,572,000
Foreign Tax Authority
Income Tax [Line Items]
Income (loss) before income taxes, equity in non-consolidated affiliates and noncontrolling interest			(11,709,000)	$ 39,025,000	$ (33,055,000)
Operating loss carryforwards	153,021,000		153,021,000
Canada
Income Tax [Line Items]
Indefinite loss carryforwards	89,258,000		89,258,000
State and Local Jurisdiction [Member]
Income Tax [Line Items]
Operating loss carryforwards	118,575,000		118,575,000
Canada Revenue Agency [Member]
Income Tax [Line Items]
Change to valuation allowance			49,447,000
Valuation allowance, deferred tax asset, increase (decrease), amount			(49,447,000)
Minimum
Income Tax [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	400,000		400,000
Maximum
Income Tax [Line Items]
Decrease in Unrecognized Tax Benefits is Reasonably Possible	$ 500,000		$ 500,000

Discontinued Operations - Text

Discontinued Operations - Textual (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017USD ($)
Entity Information [Line Items]
Goodwill, Impairment Loss	$ 17,593

Debt - Schedule of Debt (Detai

Debt - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Mar. 23, 2016	Dec. 31, 2014	Dec. 31, 2013	Mar. 20, 2013
Debt [Line Items]
Debt Issuance Costs, Line of Credit Arrangements, Gross	$ (14,036)	$ (17,587)
Debt, long-term and short-term, combined amount, total	954,107	882,413
Capital Lease Obligations	478	706
Debt and capital lease obligations	954,585	883,119
Less: Current portion	(356)	(313)
Long-term debt, less current portion	954,229	882,806
Six Point Five Zero Percentage Notes [Domain]
Debt [Line Items]
Senior notes	$ 900,000	900,000
Stated interest rate	6.50%		6.50%
6.75% Notes
Debt [Line Items]
Stated interest rate				6.75%	6.75%	6.75%
Wells Fargo Capital Finance, Llc [Member] | Revolving Credit Facility [Member]
Debt [Line Items]
Long-term Line of Credit	$ 68,143	$ 0

Debt - Schedule of Future Prin

Debt - Schedule of Future Principal Repayments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Debt Disclosure [Abstract]
2015	$ 356
2016	101
2017	68,164
2018	0
2019	0
2024 and thereafter	900,000
Future principal repayments of long term debt including capital lease obligations	$ 968,621

Debt - Schedule of Future Mini

Debt - Schedule of Future Minimum Lease Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Debt Disclosure [Abstract]
2015	$ 356
2016	101
2017	21
2018	0
2019	0
2024 and thereafter	0
Capital Leases, Future Minimum Payments, Net Minimum Payments	478
Less: imputed interest	(42)
Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments	436
Less: current portion	(356)	$ (313)
Capital leases, future minimum payments due, total	80
Current	356	313
Long-term	122	393
Capital Lease Obligations	$ 478	$ 706

Debt - Textual (Details)

Debt - Textual (Details)	Mar. 23, 2016USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Dec. 31, 2020	Mar. 12, 2019USD ($)	May 03, 2016USD ($)	Dec. 31, 2014	Dec. 31, 2013	Mar. 20, 2013
Debt [Line Items]
Interest expense, debt, total		$ 64,420,000	$ 62,001,000	$ 56,468,000
Loss on redemption of Notes		0	0	(33,298,000)
Interest expense amortization of debt premium				(312,000)
Income attributable to fair value adjustments		(374,000)	(4,819,000)	8,227,000
Amortization of Debt Issuance Costs		3,193,000	3,022,000	3,022,000
Letters of credit outstanding, amount		4,701,000
Outstanding Checks		$ 40,271,000	$ 41,989,000
Wells Fargo Capital Finance, LLC
Debt [Line Items]
Line of Credit Facility, Description			On March 20, 2013, MDC, Maxxcom Inc. (a subsidiary of MDC) and each of their subsidiaries party thereto entered into an amended and restated, $225 million senior secured revolving credit agreement due 2018 (the Credit Agreement) with Wells Fargo Capital Finance, LLC, as agent, and the lenders from time to time party thereto. Advances under the Credit Agreement will be used for working capital and general corporate purposes, in each case pursuant to the terms of the Credit Agreement. Capitalized terms used in this section and not otherwise defined have the meanings set forth in 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 1.25% in the case of Base Rate Loans and 2.00% 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.
6.75% Notes
Debt [Line Items]
Stated interest rate								6.75%	6.75%	6.75%
Loss on redemption of Notes				$ 33,298,000
Debt instrument, percentage of redemption price, redemption date one	103.375%
Six Point Five Zero Percentage Notes [Domain]
Debt [Line Items]
Stated interest rate	6.50%	6.50%
Debt instrument, face amount	$ 900,000
Debt instrument, redemption date, one			May 1, 2019
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%
Revolving Credit Facility [Member] | Wells Fargo Capital Finance, LLC
Debt [Line Items]
Maximum borrowing capacity							$ 325,000,000
Net leverage ratio							5.5
Revolving Credit Facility [Member] | Wells Fargo Capital Finance, LLC | Base Rate
Debt [Line Items]
Stated interest rate				0.75%
Revolving Credit Facility [Member] | Wells Fargo Capital Finance, LLC | London Interbank Offered Rate (LIBOR)
Debt [Line Items]
Stated interest rate			1.50%
Interest Expense [Member] | Fixed Payment [Member]
Debt [Line Items]
Income attributable to fair value adjustments		$ 87,000	$ 100,000	$ 255,000
Scenario, Forecast [Member] | Line of Credit [Member] | Amendment, Credit Agreement [Member]
Debt [Line Items]
Net leverage ratio					5.5
Subsequent Event [Member] | Line of Credit [Member] | Amendment, Credit Agreement [Member]
Debt [Line Items]
Maximum borrowing capacity						$ 250,000,000
Net leverage ratio						6.25

Share Capital - Textual (Detai

Share Capital - Textual (Details)	12 Months Ended
	Dec. 31, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares
Share Capital [Line Items]
Proceeds from exercise of options | $		$ 0	$ 0
Stock-based compensation | $	$ 5,892,000	5,335,000	5,808,000
Tax benefit from compensation expense | $	$ 472,000	$ 1,401,000	2,030,000
Employee Stock Incentive Plan
Share Capital [Line Items]
Number of shares authorized | shares	15,650,000
Employee Stock Option
Share Capital [Line Items]
Compensation cost not yet recognized | $	$ 225,000
Compensation cost not yet recognized, period	3 years
Weighted average price per share, options | $ / shares	$ 2.23	$ 0
Expected term	4 years 11 months
Risk free interest rate	2.90%
Expected volatility rate	52.90%
Dividend yield	0.00%
Award vesting period (years)	3 years
Options, outstanding, weighted average remaining contractual term	3 years
Number outstanding, expired and cancelled | shares	0
Options, exercisable, intrinsic value | $		$ 125,000	471,000
Options outstanding, intrinsic value | $	$ 0
Options vest | shares	111,866
Number outstanding, granted | shares	0
Restricted Stock And Restricted Stock Units
Share Capital [Line Items]
Equity instruments other than options, vested in period, fair value | $	$ 3,583,000	$ 7,316,000	$ 6,272,000
Stock Appreciation Rights (SARs)
Share Capital [Line Items]
Weighted average grant date fair value, granted | $ / shares	$ 0
Weighted average price per share | $ / shares	$ 2.35	$ 2.35
Equity instruments other than options, outstanding, weighted average remaining contractual terms	1 year 1 month
Compensation cost not yet recognized, period	1 year 1 month
Expected term	4 years
Risk free interest rate	1.70%
Expected volatility rate	46.20%
Dividend yield	0.00%
Number outstanding, expired and cancelled | shares	0
Options vest | shares	0		0
Number outstanding, granted | shares	0
Outstanding, intrinsic value | $	$ 0
Nonvested awards, compensation not yet recognized, share-based awards other than options | $	$ 213,000
Time Based Awards | Employee Stock Option
Share Capital [Line Items]
Weighted average grant date fair value, granted | $ / shares	$ 7.38	8.98
Weighted average price per share | $ / shares	$ 9.83	11.94	$ 12.53
Compensation cost not yet recognized | $	$ 2,325,000
Compensation cost not yet recognized, period	1 year 11 months 23 days
Time Based Awards | Restricted Stock And Restricted Stock Units
Share Capital [Line Items]
Equity instruments other than options, outstanding, weighted average remaining contractual terms	1 year 11 months 23 days
Performance Shares | Employee Stock Option
Share Capital [Line Items]
Weighted average grant date fair value, granted | $ / shares	$ 9.17
Weighted average price per share | $ / shares	$ 9.15	$ 0	$ 14
Compensation cost not yet recognized | $	$ 260,000
Common Class A
Share Capital [Line Items]
Number of votes per share	1
Common Stock,value (in dollars per share) | $ / shares	$ 0
Common stock, shares issued | shares	57,517,568	56,371,376
Common stock, shares outstanding | shares	57,517,568	56,371,376
Common Class B
Share Capital [Line Items]
Number of votes per share	20
Common Stock,value (in dollars per share) | $ / shares	$ 0
Common stock, shares issued | shares	3,755	3,755
Common stock, shares outstanding | shares	3,755	3,755

Share Capital - Schedule of Sh

Share Capital - Schedule of Share Based Compensation Performance and Time Based (Details) - Employee Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number outstanding, beginning balance	0
Weighted average price per share, beginning balance	$ 0	$ 14
Number outstanding, granted	503,321	0
Weighted average grant date fair value, granted	$ 9.17
Number outstanding, vested	(4,444)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 10.30
Number outstanding, forfeited	(45,965)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 9.29
Number outstanding, ending balance	452,912	0
Weighted average grant date fair value, ending balance	$ 9.15	$ 0
Time Based Awards
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Number outstanding, beginning balance	785,085
Weighted average price per share, beginning balance	$ 11.94	12.53
Number outstanding, granted	156,440
Weighted average grant date fair value, granted	$ 7.38	$ 8.98
Number outstanding, vested	(239,085)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 14.99
Number outstanding, forfeited	(75,500)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 9.75
Number outstanding, ending balance	626,940	785,085
Weighted average grant date fair value, ending balance	$ 9.83	$ 11.94

Share Capital - Schedule of _2

Share Capital - Schedule of Shared Based Compensation, Stock Options (Details) - Employee Stock Option	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number outstanding, beginning balance | shares	0
Weighted average price per share, beginning balance	$ 0
Weighted average price per share, beginning balance	$ 0
Options vest | shares	111,866
Weighted average price per share, granted	$ 2.23
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Weighted Average Grant Date Fair Value	0
Weighted average price per share, vested	4.85
Weighted average price per share, forfeited	$ 0
Number outstanding, granted | shares	0
Weighted average price per share, granted	$ 0
Number outstanding, exercised | shares	0
Weighted average price per share, exercised	$ 0
Number outstanding, expired and cancelled | shares	0
Weighted average price per share, expired and cancelled	$ 0
Number outstanding, ending balance | shares	111,866
Weighted average price per share, ending balance	$ 4.85

Share Capital - Schedule of _3

Share Capital - Schedule of Share Based Compensation, Stock Appreciation Rights (Details) - $ / shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Appreciation Rights (SARs) [Member]
Stock Appreciation Rights [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	250,800	327,500
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 6.60	$ 6.60
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	0		0
Weighted average price per share, vested	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	0
Share-based Compensation Arrangement by Share-based Payment Award, Stock Appreciation Rights, Outstanding [Roll Forward]
Weighted average price per share, beginning balance	2.35
Weighted average grant date fair value, granted	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(76,700)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 2.35
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 6.60
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 0
Employee Stock Option
Stock Appreciation Rights [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	111,866	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 4.85	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested, Number of Shares	(111,866)
Weighted average price per share, vested	$ 4.85
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Stock Appreciation Rights, Outstanding [Roll Forward]
Weighted average price per share, ending balance	$ 2.23	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	0
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 0

Convertible Preference Shares_2

Convertible Preference Shares (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 14, 2019	Mar. 07, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Preferred Units [Line Items]
Stock Issued During Period, Value, Convertible Preferred Shares			$ (97)
Accretion on Convertible Preferred Shares			(8,355)	$ 6,352	$ 0
Convertible preference shares
Preferred Units [Line Items]
Proceeds from Issuance of Convertible Preferred Stock			$ 0	$ 95,000	$ 0
Convertible Preference Shares | Convertible preference shares
Preferred Units [Line Items]
Stock Issued During Period, Shares, Convertible Preferred Shares		95,000
Proceeds from Issuance of Convertible Preferred Stock		$ 95,000
Stock Issued During Period, Value, Convertible Preferred Shares		$ 90,123
Preferred Stock, Conversion Price, Preference Per Share	$ 7.42	$ 10
Preferred Stock, Accretion Rate, Preference Per Share			$ 7.55	$ 6,970
Accretion on Convertible Preferred Shares			$ (8,355)	$ (36,254)
Preferred Stock, Liquidation Preference, Value				$ 109,707
Subsequent Event [Member] | Convertible Preference Shares | Series 6 Convertible Preferred Shares [Member]
Preferred Units [Line Items]
Proceeds from Issuance of Convertible Preferred Stock	$ 50,000
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Preferred Stock, Accretion Percentage, Preference	8.00%
Preferred Stock, Conversion Basis, Common Stock Class A Closing Trade Price	125.00%
Preferred stock dividend rate	7.00%

Fair Value Measurements - Fair

Fair Value Measurements - Fair Value Measurements Measured on a Recurring Basis (Details) - Six Point Five Zero Percentage Notes [Domain] - Fair Value, Inputs, Level 1 - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Liabilities:
Long term debt, carrying amount	$ 900,000	$ 900,000
Long term debt, fair value	$ 834,750	$ 904,500

Fair Value Measurements - Sche

Fair Value Measurements - Schedule of Changes to Deferred Acquisition Consideration (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability Value	$ 82,598,000	$ 119,086,000	$ 82,598,000	$ 119,086,000	$ 224,754,000
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			122,426,000
Other			374,000	4,819,000	$ (8,227,000)
Ending balance of contingent payments	83,695,000	122,426,000	83,695,000	122,426,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			(54,947,000)	(110,234,000)
Additions - acquisition and step-up transactions			14,943,000	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings			3,512,000	3,273,000
Foreign translation adjustment			4,000	1,293,000
Fixed payments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance of contingent payments			3,340,000
Ending balance of contingent payments	1,097,000	3,340,000	1,097,000	3,340,000
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements			6,000
Contingent Payment [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Other	$ (8,979,000)	$ (18,173,000)	$ 3,679,000	$ 6,021,000

Fair Value Measurements - Text

Fair Value Measurements - Textual (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Stock Authorized During Period, Value, To be Issued		$ 27,852,000
Stock Issued During Period, Shares, New Issues			0	0
Business Combination, Contingent Consideration, Liability	$ 83,695,000	122,426,000
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments	$ 0
Stock Issued During Period, Shares, New Issues			691,559
Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments		3,353,939
Common Class A | Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments		$ 28,727,000	$ 10,458,000

Segment Information - Schedule

Segment Information - Schedule of Segment Reporting Information, by Segment (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2018USD ($)segmentreportable_segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Segment Reporting Information [Line Items]
Number of reportable segments | reportable_segment									4
Services	$ 393,662,000	$ 375,830,000	$ 379,743,000	$ 326,968,000	$ 402,747,000	$ 375,800,000	$ 390,532,000	$ 344,700,000	$ 1,476,203,000	$ 1,513,779,000	$ 1,385,785,000
Office and general expenses									349,056,000	310,455,000	306,251,000
Depreciation and amortization									46,196,000	43,474,000	46,446,000
Goodwill, Impairment Loss									74,560,000	3,238,000
Operating income									9,696,000	131,959,000	48,431,000
Other Income (Expense):
Other income, net									230,000	1,346,000	414,000
Foreign Currency Transaction Gain (Loss), before Tax	(13,324,000)				(660,000)				(23,258,000)	18,137,000	(213,000)
Interest expense, finance charges, and loss on redemption of notes, net									(67,075,000)	(64,364,000)	(65,050,000)
Gain (Loss) on Repurchase of Debt Instrument									0	0	(33,298,000)
Income (loss) before income taxes and equity in earnings of non-consolidated affiliates									(80,407,000)	87,078,000	(49,716,000)
Income tax benefit									(31,603,000)	168,064,000	9,404,000
Income (loss) before equity in earnings of non-consolidated affiliates									(112,010,000)	255,142,000	(40,312,000)
Equity in losses of non-consolidated affiliates									62,000	2,081,000	(309,000)
Income (loss) from continuing operations	(75,713,000)	(13,667,000)	5,951,000	(28,519,000)	231,455,000	21,984,000	13,467,000	(9,683,000)	(111,948,000)	257,223,000	(40,621,000)
Stock-based compensation									5,892,000	5,335,000	5,808,000
Capital expenditures from continuing operations									20,264,000	32,958,000	29,432,000
Intangible Assets, Net (Including Goodwill)	808,720,000				906,540,000				808,720,000	906,540,000
Total assets	1,611,573,000				1,698,892,000				1,611,573,000	1,698,892,000
Net Income (Loss) Attributable to Noncontrolling Interest									(11,785,000)	(15,375,000)	(5,218,000)
Net income (loss) attributable to MDC Partners Inc.	(81,598,000)	$ (16,125,000)	$ 3,406,000	$ (29,416,000)	222,668,000	$ 18,493,000	$ 11,253,000	$ (10,566,000)	(123,733,000)	241,848,000	(45,839,000)
Share-based Compensation	$ 1,534,000				$ 7,480,000				18,416,000	24,350,000	21,003,000
Global Integrated Agencies [Member]
Segment Reporting Information [Line Items]
Services									698,872,000	797,347,400	712,793,000
Depreciation and amortization									23,571,000	23,831,000	21,555,000
Goodwill, Impairment Loss									17,828,000	2,741,000
Operating income									44,868,000	71,857,000	59,193,000
Other Income (Expense):
Capital expenditures from continuing operations									10,088,000	20,760,000	16,486,000
Share-based Compensation									$ 8,521,000	15,225,000	12,177,000
Number of Operating Segments | segment									5
All Other [Domain]
Segment Reporting Information [Line Items]
Goodwill, Impairment Loss									$ 4,691,000	0
Domestic Creative Agencies [Member]
Segment Reporting Information [Line Items]
Services									102,063,000	104,417,400	97,199,000
Depreciation and amortization									1,583,000	1,582,000	1,811,000
Goodwill, Impairment Loss									0	0
Operating income									18,552,000	19,333,000	18,089,000
Other Income (Expense):
Capital expenditures from continuing operations									951,000	1,168,000	1,153,000
Share-based Compensation									$ 1,100,000	887,000	651,000
Number of Operating Segments | segment									5
Specialist Communications [Member]
Segment Reporting Information [Line Items]
Services									$ 179,065,000	172,565,000	170,285,000
Depreciation and amortization									4,252,000	4,714,000	6,637,000
Goodwill, Impairment Loss									0	0
Operating income									18,629,000	20,728,000	1,940,000
Other Income (Expense):
Capital expenditures from continuing operations									3,618,000	1,288,000	2,741,000
Share-based Compensation									$ 714,000	2,954,000	3,629,000
Number of Operating Segments | segment									5
Media Services [Member]
Segment Reporting Information [Line Items]
Services									$ 140,753,000	166,216,000	157,696,000
Depreciation and amortization									3,119,000	4,052,000	6,091,000
Goodwill, Impairment Loss									52,041,000	497,000
Operating income									(51,196,000)	13,126,000	5,554,000
Other Income (Expense):
Capital expenditures from continuing operations									966,000	3,842,000	5,266,000
Share-based Compensation									$ 318,000	656,000	318,000
Number of Operating Segments | segment									2
All Other [Member]
Segment Reporting Information [Line Items]
Services									$ 355,450,000	273,234,000	247,812,000
Depreciation and amortization									12,909,000	8,197,000	8,768,000
Operating income									34,000,000	47,771,000	7,773,000
Other Income (Expense):
Capital expenditures from continuing operations									4,574,000	5,877,000	3,753,000
Share-based Compensation									3,104,000	2,494,000	1,703,000
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization									762,000	1,098,000	1,584,000
Operating income									(55,157,000)	(40,856,000)	(44,118,000)
Other Income (Expense):
Capital expenditures from continuing operations									67,000	23,000	33,000
Share-based Compensation									$ 4,659,000	$ 2,134,000	$ 2,525,000

Segment Information - Addition

Segment Information - Additional Information (Details)	12 Months Ended
	Dec. 31, 2018reportable_segment
Segment Reporting Information [Line Items]
Number of reportable segments	4

Segment Information - Schedu_2

Segment Information - Schedule of Fixed Assets, Goodwill and Intangibles, Net (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Long-lived Assets	$ 88,189				$ 90,306				$ 88,189	$ 90,306
Intangible Assets, Net (Including Goodwill)	808,720				906,540				808,720	906,540
Revenue	393,662	$ 375,830	$ 379,743	$ 326,968	402,747	$ 375,800	$ 390,532	$ 344,700	1,476,203	1,513,779	$ 1,385,785
United States
Segment Reporting Information [Line Items]
Long-lived Assets	76,781				77,163				76,781	77,163
Intangible Assets, Net (Including Goodwill)	679,344				706,241				679,344	706,241
Revenue									1,153,192	1,172,364	1,103,714
Canada
Segment Reporting Information [Line Items]
Long-lived Assets	4,779				5,638				4,779	5,638
Intangible Assets, Net (Including Goodwill)	61,748				127,014				61,748	127,014
Revenue									124,000	123,092	124,101
Other Geographical Location
Segment Reporting Information [Line Items]
Long-lived Assets	6,629				7,505				6,629	7,505
Intangible Assets, Net (Including Goodwill)	$ 67,628				$ 73,285				67,628	73,285
Revenue									$ 199,011	$ 218,323	$ 157,970

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Director of Operations, Attention Partners [Member] | Total Compensation [Member]
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 172,000	$ 155,000

Commitments, Contingencies an_3

Commitments, Contingencies and Guarantees - Textual (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Redeemable Noncontrolling Interests	$ 51,546	$ 62,886
Letters of credit outstanding, amount	4,701
Operating leases, rent expense	65,093	64,086	$ 56,725
Operating leases, income statement, sublease revenue	3,671	$ 2,797	$ 3,027
Future sublease income receivable	15,930
Investments [Member]
Temporary Equity [Line Items]
Investment commitments	$ 40

Commitments, Contingencies an_4

Commitments, Contingencies and Guarantees - Schedule of Future Minimum Rental Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2015	$ 58,015
2016	55,211
2017	45,974
2018	40,387
2019	38,348
2024 and thereafter	107,975
Future minimum payments due, total	$ 345,910

New Accounting Pronouncements_2

New Accounting Pronouncements New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase in tax expense due to GILTI										$ 710
Services	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 402,747	$ 375,800	$ 390,532	$ 344,700		1,476,203	$ 1,513,779	$ 1,385,785
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification										(1,170)
Payment for Contingent Consideration Liability, Operating Activities										29,141	42,790	44,914
Net Cash Provided by (Used in) Operating Activities										17,280	71,786	(45,907)
Payment for Contingent Consideration Liability, Investing Activities										61,313	99,873	135,693
Cost of Goods and Services Sold	256,088	$ 238,690	$ 253,390	$ 243,030	268,673	$ 249,418	$ 267,822	$ 237,563		991,198	1,023,476	936,133
Operating Income (Loss)										9,696	131,959	48,431
Net Income (Loss) Available to Common Stockholders, Basic										$ (132,088)	205,594	(45,839)
Earnings Per Share, Basic and Diluted										$ (2.31)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Services										$ 1,527,839
Cost of Goods and Services Sold										1,053,556
Operating Income (Loss)										(1,026)
Net Income (Loss) Available to Common Stockholders, Basic										$ (138,971)
Earnings Per Share, Basic and Diluted										$ (2.43)
Accounting Standards Update 2016-18 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Restricted Cash	$ 3,900				$ 4,600					$ 3,900	4,600	5,300
Accounting Standards Update 2016-15 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net Cash Provided by (Used in) Operating Activities										(29)	$ (42,790)	$ (44,914)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Services										51,636
Cost of Goods and Services Sold										62,358
Operating Income (Loss)										(10,722)
Net Income (Loss) Available to Common Stockholders, Basic										$ (6,883)
Earnings Per Share, Basic and Diluted										$ (0.12)
Accumulated Deficit
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
New Accounting Pronouncement or Change in Accounting Principle, Effect of Adoption, Quantification									$ (1,170)	$ (1,170)

New Accounting Pronouncements A

New Accounting Pronouncements Adoption of 606 (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 402,747	$ 375,800	$ 390,532	$ 344,700	$ 1,476,203	$ 1,513,779	$ 1,385,785
Earnings Per Share, Basic and Diluted									$ (2.31)
Cost of Goods and Services Sold	$ 256,088	$ 238,690	$ 253,390	$ 243,030	$ 268,673	$ 249,418	$ 267,822	$ 237,563	$ 991,198	1,023,476	936,133
Operating Income (Loss)									9,696	131,959	48,431
Net Income (Loss) Available to Common Stockholders, Basic									(132,088)	$ 205,594	$ (45,839)
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services									$ 1,527,839
Earnings Per Share, Basic and Diluted									$ (2.43)
Cost of Goods and Services Sold									$ 1,053,556
Operating Income (Loss)									(1,026)
Net Income (Loss) Available to Common Stockholders, Basic									(138,971)
Accounting Standards Update 2014-09 [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Services									$ 51,636
Earnings Per Share, Basic and Diluted									$ (0.12)
Cost of Goods and Services Sold									$ 62,358
Operating Income (Loss)									(10,722)
Net Income (Loss) Available to Common Stockholders, Basic									$ (6,883)

Employee Benefit Plans - Sched

Employee Benefit Plans - Schedule of Net Periodic Pension Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Service cost	$ 0	$ 0	$ 0
Interest cost on benefit obligation	1,641	1,725	1,855
Expected return on plan assets	(1,948)	(1,830)	(1,863)
Curtailment and settlements	1,039	0	929
Amortization of actuarial losses	258	222	137
Net periodic benefit cost	$ 990	$ 117	$ 1,058

Employee Benefit Plans - Sch_2

Employee Benefit Plans - Schedule of Defined Benefit Plan Amounts in Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Curtailment/settlement	$ 0	$ 0
Current year actuarial (gain) loss	(520)	1,558
Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss), Amortization of Actuarial Gain (Loss), Before Tax	258	222
Total recognized in other comprehensive (income) loss	(778)	1,336
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$ 212	$ 1,453

Employee Benefit Plans - Sch_3

Employee Benefit Plans - Schedule of Benefit Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Liability, Defined Benefit Plan, Noncurrent	$ 14,757	$ 15,773
Change in benefit obligation:
Benefit obligation, Beginning balance	43,750	40,722
Service Cost	0	0	$ 0
Interest Cost	1,641	1,725	1,855
Actuarial losses	(3,522)	3,088
Benefit obligation, Ending balance	37,938	43,750	40,722
Change in plan assets:
Fair value of plan assets, Beginning balance	27,977	24,482
Actual return on plan assets	(2,093)	3,360
Employer contributions	1,228	1,920
Fair value of plan assets, Ending balance	23,181	27,977	$ 24,482
Defined Benefit Plan, Benefit Obligation, Benefits Paid	3,931	1,785
Defined Benefit Plan, Plan Assets, Benefits Paid	$ 3,931	$ 1,785

Employee Benefit Plans - Sch_4

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

Employee Benefit Plans - Sch_5

Employee Benefit Plans - Schedule of Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Defined Benefit Plan, Accumulated Other Comprehensive Income Net Settlement and Curtailment gain (loss), net of tax	$ 12,878	$ 13,656
Accumulated Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net of Tax	$ 12,878	$ 13,656

Employee Benefit Plans - Sch_6

Employee Benefit Plans - Schedule of Assumptions Used to Determine Benefit Obligation (Details)	Dec. 31, 2018	Dec. 31, 2017
Retirement Benefits [Abstract]
Discount rate	4.42%	3.83%

Employee Benefit Plans - Sch_7

Employee Benefit Plans - Schedule of Assumptions Used to Determine Net Periodic Costs (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate	3.83%	4.32%	4.69%
Expected return on plan assets	7.00%	7.40%	7.40%

Employee Benefit Plans - Sch_8

Employee Benefit Plans - Schedule of Changes in Fair Value of Plan Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 23,181	$ 27,977	$ 24,482
Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,445	26,282
Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,736	1,695
Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	23,181	27,977
Fair Value, Inputs, Level 1 | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21,445	26,282
Fair Value, Inputs, Level 1 | Money Market Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,736	1,695
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, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	100.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	100.00%	100.00%
Cash and Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	7.50%	6.10%
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	65.00%
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	67.00%	68.90%

Employee Benefit Plans - Sc_10

Employee Benefit Plans - Schedule of Expected Benefit Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Estimated Future Benefit Payments for FYE 12/31
2015	$ 1,690
2016	1,857
2017	1,848
2018	1,912
2019	2,139
2024 – 2027	$ 11,047

Employee Benefit Plans - Textu

Employee Benefit Plans - Textual (Details) - USD ($) $ in Thousands	Jan. 01, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Target Allocation		100.00%
Estimate of net actuarial losses reclassified from AOCI in the next fiscal year		$ 555	$ (1,336)
Other comprehensive loss, before reclassifications, net of tax		(6,119)	(1,206)
Current employer pension plan contributions		1,228	$ 1,920
Scenario, Forecast [Member] | Reclassification out of Accumulated Other Comprehensive Income [Domain]
Defined Benefit Plan Disclosure [Line Items]
Estimate of net actuarial losses reclassified from AOCI in the next fiscal year	$ 266
Other comprehensive loss, before reclassifications, net of tax	$ 266
Pension Plan, Defined Benefit
Defined Benefit Plan Disclosure [Line Items]
Current employer pension plan contributions		1,228
Expected pension plan contribution		$ 1,156

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Defined benefit pension, balance January 1	$ 13,656	$ 12,320
Foreign currency translation, balance January 1	11,702	10,496
Total, balance January 1	(1,954)	(1,824)
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	6,119	1,206
Total, other comprehensive income (loss) before reclassifications	6,119	1,206
Amounts reclassified from accumulated other comprehensive income (loss)	0	0
Amounts reclassified from accumulated other comprehensive income (loss)	555	(1,336)
Total, amounts reclassified from accumulated other comprehensive income (loss)	555	(1,336)
Defined benefit pension, other comprehensive income (loss)	555	(1,336)	$ (3,101)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax, Portion Attributable to Parent	6,119	1,206
Total, other comprehensive income (loss)	6,674	(130)
Defined benefit pension, balance December 31	13,101	13,656	12,320
Foreign currency translation, balance December 31	17,821	11,702	10,496
Total, balance December 31	$ 4,720	$ (1,954)	$ (1,824)

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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Services	$ 393,662	$ 375,830	$ 379,743	$ 326,968	$ 402,747	$ 375,800	$ 390,532	$ 344,700	$ 1,476,203	$ 1,513,779	$ 1,385,785
Cost of services sold	256,088	238,690	253,390	243,030	268,673	249,418	267,822	237,563	991,198	1,023,476	936,133
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	(75,713)	(13,667)	5,951	(28,519)	231,455	21,984	13,467	(9,683)	(111,948)	257,223	(40,621)
Net income (loss) attributable to MDC Partners Inc.	$ (81,598)	$ (16,125)	$ 3,406	$ (29,416)	$ 222,668	$ 18,493	$ 11,253	$ (10,566)	$ (123,733)	$ 241,848	$ (45,839)
Continuing operations (in dollars per share)									$ (2.31)	$ 3.72	$ (0.89)
Net income (loss) (in dollars per share)	$ (1.46)	$ (0.32)	$ 0.02	$ (0.56)	$ 3.33	$ 0.25	$ 0.14	$ (0.21)	(2.31)	3.72	(0.89)
Continuing operations (in dollars per share)									(2.31)	3.71	(0.89)
Net income (loss) (in dollars per share)	$ (1.46)	$ (0.32)	$ 0.02	$ (0.56)	$ 3.30	$ 0.24	$ 0.14	$ (0.21)	$ (2.31)	$ 3.71	$ (0.89)

Quarterly Results of Operatio_4

Quarterly Results of Operations - Textual (Details) - USD ($)	3 Months Ended			12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition, Contingent Consideration [Line Items]
Foreign exchange gain (loss)	$ 13,324,000	$ 660,000		$ 23,258,000	$ (18,137,000)	$ 213,000
Cost of services sold	1,534,000	7,480,000		18,416,000	24,350,000	21,003,000
Income attributable to fair value adjustments				(374,000)	(4,819,000)	8,227,000
Asset Impairment Charges	56,732,000			80,057,000	4,415,000	$ 48,524,000
Goodwill, Impairment Loss				74,560,000	3,238,000
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	49,447,000	226,466,000
Contingent Payment [Member]
Business Acquisition, Contingent Consideration [Line Items]
Income attributable to fair value adjustments	$ 8,979,000	18,173,000		(3,679,000)	(6,021,000)
All Other [Domain]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill, Impairment Loss				$ 4,691,000	$ 0
Experiential and Non-material [Member]
Business Acquisition, Contingent Consideration [Line Items]
Goodwill, Impairment Loss		$ 18,893,000	$ 29,631,000

VALUATION AND QUALIFYING ACCO_2

VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	$ 2,453	$ 1,523	$ 1,306
Charged to Costs and Expenses	1,538	1,989	1,053
Removal of Uncollectible Receivables	(1,795)	(924)	(830)
Translation Adjustments Increase (Decrease)	(317)	(135)	(6)
Balance at the End of Period	1,879	2,453	1,523
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Period	19,032	248,867	247,967
Charged to Costs and Expenses	49,447	(230,358)	6,605
Other	0	4,108	(6,032)
Translation Adjustments Increase (Decrease)	0	(3,585)	327
Balance at the End of Period	$ 68,479	$ 19,032	$ 248,867

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	Mar. 14, 2019	Dec. 31, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Preferred stock, shares issued		95,000	95,000
Common Class A | Subsequent Event [Member]
Subsequent Event [Line Items]
Price per share	$ 3.50
Common Class A | Common Stock | Subsequent Event [Member]
Subsequent Event [Line Items]
Class A shares issued	14,285,714
Proceeds from sale of Class A shares	$ 50
Series 6 Convertible Preferred Shares [Member] | Convertible Preference Shares | Subsequent Event [Member]
Subsequent Event [Line Items]
Series 6 convertible preference shares issued	50,000
Proceeds from issuance of Series 6 convertible preference shares	$ 50
Preferred Stock, Convertible Preference Shares, Convertible By Holder, Term	1 year
Preferred Stock, Liquidation Preference Per Share	$ 1,000
Initial conversion price per Preference Share	$ 5
Accretion rate of preferred stock	8.00%
Accretion period of preferred stock	5 years
Term preferred stock convertible at company's option	2 years
Percentage of conversion price	125.00%
Preferred stock dividend rate	7.00%
Percent of ownership in common shares triggering limit to conversion of preferred shares	19.90%
Preferred stock conversion ratio to common stock	1

Other Income (Details)

Other Income (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other income, net			$ 230	$ 1,346	$ 414
Foreign Currency Transaction Gain (Loss), before Tax	$ (13,324)	$ (660)	$ (23,258)	$ 18,137	$ (213)