UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	AOCI Attributable to Parent [Member]	Accumulated Other Comprehensive Income (Loss)	MDC Partners Inc. Shareholders' Deficit	Noncontrolling Interest	Common Class A [Member] Common Stock	Series 4 Convertible Preferred Stock [Member] Convertible Preferred Stock	Contingent Consideration, Liability Settlements [Domain] Series 4 Convertible Preferred Stock [Member] Convertible Preferred Stock
Balance at Dec. 31, 2017	$ (155,513)			$ 38,191	$ (340,000)	$ (1,954)		$ (213,543)	$ 58,030
Balance (in shares) at Dec. 31, 2017											95,000
Common stock, balance (in shares) at Dec. 31, 2017			56,375,131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(16,125)							(16,125)
Shares acquired and cancelled	(283)			(283)				(283)
Balance at Mar. 31, 2018	(177,940)	$ 90,123		50,619	(383,305)	(1,319)		(243,882)	65,942
Balance (in shares) at Mar. 31, 2018		95,000,000
Common stock, balance (in shares) at Mar. 31, 2018			57,515,439
Adjustments to Additional Paid in Capital, Changes due to Business Combinations								3,809
Balance at Dec. 31, 2017	(155,513)			38,191	(340,000)	(1,954)		(213,543)	58,030
Balance (in shares) at Dec. 31, 2017											95,000
Common stock, balance (in shares) at Dec. 31, 2017			56,375,131
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(42,135)
Other comprehensive loss	(898)
Balance at Sep. 30, 2018		$ 90,123
Adjustments to Additional Paid in Capital, Changes due to Business Combinations				(745)				(745)
Balance at Dec. 31, 2018	(246,967)	$ 90,123		58,579	(464,903)	4,720		(311,481)	64,514
Balance (in shares) at Dec. 31, 2018										57,517,568
Common stock, balance (in shares) at Dec. 31, 2018			57,521,323
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	2,425
Other comprehensive loss	(7,505)						$ (7,598)	(7,598)	93
Issuance of common and preference shares (in shares)		50,000,000
Issuance of common and convertible preference shares	98,620			35,997				98,620				$ 62,623
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			566,932
Shares acquired and cancelled	(577)			(577)				(577)
Shares acquired and cancelled (in shares)			(227,552)
Stock-based compensation	1,918			1,918				1,918
Changes in redemption value of redeemable noncontrolling interests	3,496			3,496				3,496
Changes in ownership interest									(24,642)
Balance at Sep. 30, 2019	$ (174,295)	$ 152,746		$ 98,364	$ (462,483)	$ (2,878)		$ (214,251)	$ 39,956
Balance (in shares) at Sep. 30, 2019		145,000,000									145,000,000
Common stock, balance (in shares) at Sep. 30, 2019			72,146,417