Segment Reporting - Schedule of Reportable Operating Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025
Segment Reporting [Line Items]
Revenue	$ 337,318	$ 284,288	$ 795,722	$ 668,346
Operating expenses:
Operating income	102,440	117,334	117,598	64,814
Interest income	1,581	881	4,957	3,111
Interest expense	(5,739)	(20)	(17,860)	(267)
Other income, net	1,313	786	5,284	3,079
Income before income tax expense	99,595	118,981	109,979	70,737
Income tax expense	31,627	7,870	34,367	5,033
Net loss attributable to Andersen Group Inc.	(8,981)		(9,495)
Reportable Segment
Segment Reporting [Line Items]
Revenue	337,318	284,288	795,722	668,346
Operating expenses:
Personnel costs	188,190	130,463	545,294	494,573
Non-personnel and other operating costs	43,824	33,854	125,170	102,191
Depreciation and amortization	2,864	2,637	7,660	6,768
Total operating expenses	234,878	166,954	678,124	603,532
Operating income	102,440	117,334	117,598	64,814
Interest income	1,581	881	4,957	3,111
Interest expense	(5,739)	(20)	(17,860)	(267)
Other income, net	1,313	786	5,284	3,079
Income before income tax expense	99,595	118,981	109,979	70,737
Income tax expense	31,627	7,870	34,367	5,033
Net loss attributable to Andersen Group Inc.	$ 67,968	$ 111,111	$ 75,612	$ 65,704