Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended					9 Months Ended
	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2020	Sep. 30, 2019
Class of Stock [Line Items]
Net loss attributable to MDC Partners Inc.	$ 4,076		$ (1,752)			$ 4,486	$ 2,425
Numerator
Net income (loss) attributable to MDC Partners Inc. common shareholders	$ 360	$ (17,557)	$ (5,058)	$ (138,362)	$ 204,832	$ (6,042)	$ (6,506)
Denominator
Denominator for basic income (loss) per common share - weighted average common shares	73,207,619	69,132,100	72,044,480	57,218,994	55,255,797	72,713,257	68,154,306
Impact of stock options and non-vested stock under employee stock incentive plans (in shares)	269,160		0			0	0
Denominator for diluted income (loss) per common share - adjusted weighted shares and assumed conversions	73,476,779	69,132,100	72,044,480	57,218,994	55,481,786	72,713,257	68,154,306
Earnings per share, basic	$ 0	$ (250)	$ (0.07)	$ (2,420)	$ 3,710	$ (0.08)	$ (0.10)
Earnings per share, diluted	$ 0	$ (250)	$ (0.07)	$ (2,420)	$ 3,700	$ (0.08)	$ (0.10)
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	2,325,800,000					3,539,060,000
MDC Partners Inc. Shareholders' Deficit
Class of Stock [Line Items]
Net loss attributable to MDC Partners Inc.	$ 4,076		$ (1,752)			$ 4,486	$ 2,425
Series 4 Convertible Preferred Stock | Convertible Preferred Stock
Numerator
Accretion on and net income allocated to convertible preference shares	3,579		3,306			10,528	8,931
Net income allocated to convertible preference shares	$ (137)		$ 0			$ 0	$ 0
Denominator
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount			3,714,595,000				3,714,595,000