UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - 3 months ended Mar. 31, 2018 - USD ($) $ in Thousands	Total	Convertible Preferred Stock Series 4 Convertible Preferred Stock	Common Stock	Share Capital To Be Issued	Additional Paid-in Capital	Charges in Excess of Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)	MDC Partners Inc. Shareholders' Deficit	Noncontrolling Interest
Balance at Dec. 31, 2017	$ (155,513)	$ 90,220	$ 352,432		$ 0	$ (314,241)	$ (340,000)	$ (1,954)	$ (213,543)	$ 58,030
Balance (in shares) at Dec. 31, 2017		95,000	56,375,131
Common Stock, Shares, To be Issued, beginning (shares) at Dec. 31, 2017				0
Common Stock, Value, To be Issued, beginning at Dec. 31, 2017				$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(29,416)						(29,416)		(29,416)
Other comprehensive income (loss)	2,278							3,379	3,379	(1,101)
Expenses for convertible preference shares (Note 9)	(97)	$ (97)							(97)
Issuance of restricted stock	0		$ 1,097		(1,097)
Issuance of restricted stock (in shares)			109,444
Shares acquired and cancelled	(455)		$ (455)						(455)
Shares acquired and cancelled (in shares)			(48,508)
Stock-based compensation	2,217				2,217				2,217
Changes in redemption value of redeemable noncontrolling interests	(375)				(375)				(375)
Increase (decrease) in noncontrolling interests and redeemable noncontrolling interests from business acquisitions and step-up transactions	(1,166)				(1,166)				(1,166)
Changes in noncontrolling interests and redeemable noncontrolling interests from changes in ownership interest	(5,965)									(5,965)
Cumulative effect of adoption of ASC 606 (Note 14)	(1,170)						(1,170)		(1,170)
Transfer to charges in excess of capital	0				421	(421)
Balance at Mar. 31, 2018	$ (189,662)	$ 90,123	$ 353,074		$ 0	$ (314,662)	$ (370,586)	$ 1,425	$ (240,626)	$ 50,964
Balance (in shares) at Mar. 31, 2018		95,000	56,436,067
Common Stock, Shares, To be Issued, ending (shares) at Mar. 31, 2018				0
Common Stock, Value, To be Issued, ending at Mar. 31, 2018				$ 0