Transactions with Related Parties - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025	Dec. 31, 2023	Dec. 31, 2021
Related Party Transaction [Line Items]
Other income, net	$ 1,313,000	$ 786,000	$ 5,284,000	$ 3,079,000
Cost of services (excluding depreciation and amortization)	182,957,000	123,832,000	522,892,000	467,038,000
Other current liabilities	36,479,000		36,479,000		$ 5,912,000
Prepaid expenses and other current assets	35,781,000		35,781,000		29,688,000
Andersen Global And Contributing Firms
Related Party Transaction [Line Items]
Related party expenses	1,700,000	500,000	6,100,000	1,100,000
Related Party
Related Party Transaction [Line Items]
Interest income includes interest earned on loans and notes receivable from related parties	0	0	0	0
Financing receivable, before allowance for credit loss	8,115,000		8,115,000		11,648,000
Total loans and notes receivable from related parties, net of allowance for credit losses	1,273,000		1,273,000		913,000
Related Party | Member firm loans
Related Party Transaction [Line Items]
Financing receivable, before allowance for credit loss	7,035,000		7,035,000		11,035,000
Total loans and notes receivable from related parties, net of allowance for credit losses	300,000		$ 300,000		300,000
Maturity period			11 years
Related Party | Employee loans
Related Party Transaction [Line Items]
Financing receivable, before allowance for credit loss	1,080,000		$ 1,080,000		218,000
Total loans and notes receivable from related parties, net of allowance for credit losses	100,000		100,000		$ 200,000
Maturity period					5 years
Related Party | Stewardship Funds Maturing on December 31, 2029
Related Party Transaction [Line Items]
Financing receivable, before allowance for credit loss					$ 100,000	$ 2,000,000.0	$ 2,000,000.0
Financing receivable, term							30 days
Related Party | Stewardship Funds Maturing on December 31, 2033
Related Party Transaction [Line Items]
Financing receivable, before allowance for credit loss	0		0		300,000
Financing receivable, term						60 days
Related Party | Trademark and License Fees
Related Party Transaction [Line Items]
Other income, net	900,000	600,000	3,200,000	2,400,000
Cost of services (excluding depreciation and amortization)		$ 0		$ 100,000
Other current liabilities					100,000
Related Party | License Fees and Andersen Global Commitments
Related Party Transaction [Line Items]
Prepaid expenses and other current assets	5,700,000		5,700,000		4,300,000
Related Party | Andersen Global Commitments
Related Party Transaction [Line Items]
Other current liabilities	2,200,000		2,200,000		600,000
Related Party | State Tax Payments
Related Party Transaction [Line Items]
Prepaid expenses and other current assets	$ 2,700,000		$ 2,700,000		$ 2,700,000