The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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