Net (Loss) Income Per Share - Schedule of Basic and Diluted Income Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Net (loss) income attributable to Direct Digital Holdings, Inc.	$ (590)	$ 192	$ (1,365)	$ (22)
Less: net income allocated to participating securities	0	99	0	0
Less: net income allocated to participating securities	0	99	0	0
Net (loss) income allocated to Class A shareholders	(590)	93	(1,365)	(22)
Net (loss) income allocated to Class A shareholders	$ (590)	$ 93	$ (1,365)	$ (22)
Weighted average common shares outstanding - basic (in shares)	3,700,615	2,921,258	3,604,220	2,911,801
Options to purchase common stock (in shares)	0	51,180	0	0
Unvested restricted stock units (in shares)	0	140,751	0	0
Weighted average common shares outstanding - diluted (in shares)	3,700,615	3,113,189	3,604,220	2,911,801
Net loss per common share, basic (in dollars per share)	$ (0.16)	$ 0.03	$ (0.38)	$ (0.01)
Net loss per common share, diluted (in dollars per share)	$ (0.16)	$ 0.03	$ (0.38)	$ (0.01)
Class B Common Stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Options to purchase common stock (in shares)	0	0	0	0