Business Segment Information - Schedule of Financial Information about Business Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting [Abstract]
Reportable Segments Not Disclosed Flag	true
Segment Reporting Information [Line Items]
Total revenue	$ 2,297,381	$ 2,125,151	$ 1,919,793
Operations & services	842,775	792,509	740,719
Sales, marketing & client service	174,254	174,498	170,959
Technology services & infrastructure	214,349	198,788	189,536
Strategic initiatives & new business development	197,570	205,660	221,150
Corporate services & other segment expenses	60,299	54,307	40,664
Segment profit (loss)	808,134	699,389	556,765
Investment Managers
Segment Reporting Information [Line Items]
Total revenue	815,005	728,390	645,254
Operations & services	355,027	324,602	289,348
Sales, marketing & client service	42,488	40,143	35,914
Technology services & infrastructure	52,154	43,293	42,001
Strategic initiatives & new business development	29,878	33,804	42,811
Corporate services & other segment expenses	14,749	11,243	9,122
Segment profit (loss)	320,709	275,305	226,058
Private Banks
Segment Reporting Information [Line Items]
Total revenue	572,939	541,414	496,317
Operations & services	211,193	200,250	200,946
Sales, marketing & client service	40,587	41,463	37,271
Technology services & infrastructure	114,209	110,154	105,698
Strategic initiatives & new business development	85,398	85,662	86,888
Corporate services & other segment expenses	23,548	22,846	17,687
Segment profit (loss)	98,004	81,039	47,827
Investment Advisors
Segment Reporting Information [Line Items]
Total revenue	577,397	509,408	436,298
Operations & services	177,822	162,396	145,094
Sales, marketing & client service	35,437	31,872	28,547
Technology services & infrastructure	35,572	33,812	31,246
Strategic initiatives & new business development	52,263	48,526	49,657
Corporate services & other segment expenses	10,568	6,296	4,598
Segment profit (loss)	265,735	226,506	177,156
Institutional Investors
Segment Reporting Information [Line Items]
Total revenue	282,498	285,723	289,708
Operations & services	83,846	85,807	87,778
Sales, marketing & client service	39,035	41,612	52,056
Technology services & infrastructure	6,378	5,998	5,284
Strategic initiatives & new business development	13,039	14,241	14,567
Corporate services & other segment expenses	5,834	7,043	5,770
Segment profit (loss)	134,366	131,022	124,253
Investments in New Businesses
Segment Reporting Information [Line Items]
Total revenue	49,542	60,216	52,216
Operations & services	14,887	19,454	17,553
Sales, marketing & client service	16,707	19,408	17,171
Technology services & infrastructure	6,036	5,531	5,307
Strategic initiatives & new business development	16,992	23,427	27,227
Corporate services & other segment expenses	5,600	6,879	3,487
Segment profit (loss)	$ (10,680)	$ (14,483)	$ (18,529)

SEI INVESTMENTS CO 10-K