Segment Reporting - Schedule of Reconciliation (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
Revenue		$ 838,692	$ 731,593	$ 639,111
Operating expenses:
Total operating (loss) income		(135,293)	129,544	116,859
Interest income		4,166	4,524	2,660
Interest expense		(1,436)	(64)	(138)
Other income, net		5,391	3,192	1,559
(Loss) income before income tax expense		(127,172)	137,196	120,940
Income tax expense		2,997	2,395	2,257
Net loss attributable to Andersen Group Inc.	[1]	(2,324)
Reportable Segment
Segment Reporting Information [Line Items]
Revenue		838,692	731,593	639,111
Operating expenses:
Personnel costs		818,290	462,394	403,294
Non-personnel costs		146,690	131,330	111,267
Depreciation and amortization		9,005	8,325	7,691
Total operating expenses		973,985	602,049	522,252
Total operating (loss) income		(135,293)	129,544	116,859
Interest income		4,166	4,524	2,660
Interest expense		(1,436)	(64)	(138)
Other income, net		5,391	3,192	1,559
(Loss) income before income tax expense		(127,172)	137,196	120,940
Income tax expense		2,997	2,395	2,257
Net loss attributable to Andersen Group Inc.		$ (130,169)	$ 134,801	$ 118,683

[1] Represents net loss attributable to Andersen Group Inc. for the period following the IPO and Reorganization Transactions as described in Note 1 in the accompanying notes.