Noncontrolling and Redeemable Noncontrolling Interests - Changes in Noncontrolling Interests (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.	$ 6,106	$ (595)	$ 11,116	$ 407
Business acquisitions and step-up transactions, net of tax	(10,339)		(10,669)	(503)
Change from net income (loss) attributable to MDC Partners Inc. and transfers to noncontrolling interests	4,233	595	(447)	96
MDC Partners Inc. Shareholders' Deficit
Noncontrolling Interest [Line Items]
Net loss attributable to MDC Partners Inc.	6,106		11,116
Business acquisitions and step-up transactions, net of tax	$ (10,339)	$ 0	$ (10,669)	$ (503)