Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
	Dec. 31, 2025	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Numerator:
Net (loss) income	$ (23,867)	$ (130,169)	$ 134,801	$ 118,683
Net loss attributable to redeemable noncontrolling interest	(21,543)	$ (127,845)
Net loss attributable to Andersen Group Inc. stockholders, basic	(2,324)
Net loss attributable to Andersen Group Inc. stockholders, diluted	$ (23,867)
Denominator:
Weighted average number of shares of Class A common stock outstanding (in shares)	12,650,000
Effect of dilutive Class X Umbrella Units (in shares)	98,294,464
Weighted-average shares of Class A common stock outstanding, diluted (in shares)	110,944,464
Net loss per share:
Loss per share attributable to Class A common stockholders, basic (in dollars per share)	$ (0.18)
Loss per share attributable to Class A common stockholders, diluted (in dollars per share)	$ (0.22)