UNAUDITED CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' DEFICIT - USD ($) $ in Thousands	Total	Convertible Preference Shares	Common Shares	Common Stock and Other Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income	MDC Partners Inc. Shareholders' Deficit	Noncontrolling Interests	Series 4 Convertible Preferred Stock [Member] Convertible Preference Shares
Balance at Dec. 31, 2019	$ (190,575)	$ 152,746		$ 101,469	$ (480,779)	$ (4,269)	$ (230,833)	$ 40,258
Balance (in shares) at Dec. 31, 2019									145,000,000
Common stock, balance (in shares) at Dec. 31, 2019			72,154,603
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	407				407
Other comprehensive income (loss)	8,796					8,895	8,895	(99)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			760,561
Shares acquired and cancelled	(732)			(732)			(732)
Shares acquired and cancelled (in shares)			(327,774)
Stock-based compensation	1,033			1,033			1,033
Changes in redemption value of redeemable noncontrolling interests	(2,630)			(2,630)			(2,630)
Business acquisitions and step-up transactions, net of tax	(503)			(503)			(503)
Other	(402)			(403)	1	(1)	(401)	(1)
Balance at Jun. 30, 2020	(184,606)	152,746		98,234	(480,371)	4,627	(224,764)	40,158
Balance (in shares) at Jun. 30, 2020									145,000,000
Common stock, balance (in shares) at Jun. 30, 2020			72,587,390
Balance at Mar. 31, 2020	(183,944)	152,746		99,587	(479,695)	3,669	(223,693)	39,749
Balance (in shares) at Mar. 31, 2020									145,000,000
Common stock, balance (in shares) at Mar. 31, 2020			72,483,166
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	(595)				(595)
Other comprehensive income (loss)	1,367					957	957	410
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			173,334
Shares acquired and cancelled	(95)			(95)			(95)
Shares acquired and cancelled (in shares)			(69,110)
Stock-based compensation	557			557			557
Changes in redemption value of redeemable noncontrolling interests	(1,412)			(1,412)			(1,412)
Business acquisitions and step-up transactions, net of tax							0
Other	(484)			(403)	(81)	1	(483)	(1)
Balance at Jun. 30, 2020	(184,606)	152,746		98,234	(480,371)	4,627	(224,764)	40,158
Balance (in shares) at Jun. 30, 2020									145,000,000
Common stock, balance (in shares) at Jun. 30, 2020			72,587,390
Balance at Dec. 31, 2020	(408,910)	152,746		104,367	(709,751)	2,739	(449,899)	40,989
Balance (in shares) at Dec. 31, 2020									145,000,000
Common stock, balance (in shares) at Dec. 31, 2020			73,532,848
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	11,116				11,116		11,116
Other comprehensive income (loss)	(3,312)					(2,699)	(2,699)	(613)
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			1,703,093
Shares acquired and cancelled	(436)			(436)			(436)
Shares acquired and cancelled (in shares)			(109,394)
Stock-based compensation	2,529			2,529			2,529
Changes in redemption value of redeemable noncontrolling interests	2,000			2,000			2,000
Business acquisition and step-up transactions, net of tax (in shares)			2,131,574
Business acquisitions and step-up transactions, net of tax	(10,669)			(10,669)			(10,669)
Other	(10)			(8)		(1)	(9)	(1)
Balance at Jun. 30, 2021	(407,692)	152,746		97,783	(698,635)	39	(448,067)	40,375
Balance (in shares) at Jun. 30, 2021									145,000,000
Common stock, balance (in shares) at Jun. 30, 2021			77,258,121
Balance at Mar. 31, 2021	(405,583)	152,746		106,193	(704,741)	183	(445,619)	40,036
Balance (in shares) at Mar. 31, 2021									145,000,000
Common stock, balance (in shares) at Mar. 31, 2021			74,791,060
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss attributable to MDC Partners Inc.	6,106				6,106		6,106
Other comprehensive income (loss)	195					(144)	(144)	339
Issuance of restricted stock	0
Issuance of restricted stock (in shares)			380,361
Shares acquired and cancelled	(234)			(234)			(234)
Shares acquired and cancelled (in shares)			(44,874)
Stock-based compensation	1,494			1,494			1,494
Changes in redemption value of redeemable noncontrolling interests	319			319			319
Business acquisition and step-up transactions, net of tax (in shares)			2,131,574
Business acquisitions and step-up transactions, net of tax	(10,339)			(10,339)			(10,339)
Other	350			350			350
Balance at Jun. 30, 2021	$ (407,692)	$ 152,746		$ 97,783	$ (698,635)	$ 39	$ (448,067)	$ 40,375
Balance (in shares) at Jun. 30, 2021									145,000,000
Common stock, balance (in shares) at Jun. 30, 2021			77,258,121