Organization and Business Description (Details) $ / shares in Units, $ in Thousands			1 Months Ended		9 Months Ended
	Dec. 18, 2025 USD ($) $ / shares shares	Dec. 16, 2025 USD ($) shares	Aug. 31, 2026 shares	Jun. 30, 2026 shares	Sep. 30, 2026 vote office state shares
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of offices | office					28
Number of states | state					15
2025 Equity Incentive Plan | Restricted Stock Units (RSUs)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Share issued (in shares) | shares		5,440,720		61,231
TRA Parties
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest rate		85.00%
AT Umbrella LLC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Membership interest units acquired (in shares) | shares	12,650,000
AT Umbrella LLC | Capital Account Notes
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate principal amount		$ 187,800
AT Umbrella LLC | Capital Account Notes | Notes Payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Aggregate principal amount		$ 187,800
AT Umbrella LLC | Capital Account Notes | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		2 years
Interest rate		6.31%
AT Umbrella LLC | Capital Account Notes | Minimum | Notes Payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest rate		6.31%
AT Umbrella LLC | Capital Account Notes | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		7 years
Interest rate		7.50%
AT Umbrella LLC | Capital Account Notes | Maximum | Notes Payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Interest rate		7.50%
AT Umbrella LLC | Holdover Note
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		8 years
Aggregate principal amount		$ 162,300
Interest rate		7.63%
AT Umbrella LLC | Holdover Note | Notes Payable
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		8 years
Aggregate principal amount		$ 162,300
Interest rate		7.63%
Post-service obligation payment period		7 years
Management Holdco | Member Notes
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		7 years
Management Holdco | Member Notes | If Balance Is At Least $550,000
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Principal balance, threshold		$ 550
Management Holdco | Member Notes | If Balance Is At Least $550,000 | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		3 years
Management Holdco | Member Notes | If Balance Is At Least $550,000 | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		7 years
Management Holdco | Member Notes | If Balance Is Less Than $550,000
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Principal balance, threshold		$ 550
Management Holdco | Member Notes | If Balance Is Less Than $550,000 | Minimum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		2 years
Management Holdco | Member Notes | If Balance Is Less Than $550,000 | Maximum
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Debt instrument, term		7 years
Class A Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of votes | vote					1
Class A Common Stock | IPO
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds to purchase shares (in shares) | shares	12,650,000
Sale of stock, price per share (in dollars per share) | $ / shares	$ 16.00
Proceeds from issuance initial public offering	$ 188,200
Underwriting discounts and commissions	14,200
Offering costs	$ 9,900
Class A Common Stock | Over-Allotment Option
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds to purchase shares (in shares) | shares	1,650,000
Class B Common Stock
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of votes | vote					10
Class B Common Stock | Secondary Offering
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares repurchased (in shares) | shares			102,000
Class X Umbrella Units
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares converted (in shares) | shares					5,029,125
Class X Umbrella Units | Resale Offering, Selling Stockholders
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Shares converted (in shares) | shares					4,927,125
AT Umbrella LLC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity method investment, ownership percentage					16.50%
Andersen Tax Holdings LLC | Andersen Aggregator LLC
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Equity method investment, ownership percentage	100.00%
Andersen Aggregator LLC | Class B Common Stock | Andersen Group Inc
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Proceeds to purchase shares (in shares) | shares	98,302,500