Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities
Net income	$ 246,912	$ 274,181	$ 258,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	76,699	73,824	70,557
Amortization of operating lease right-of-use assets	7,523	6,639	5,853
Stock-based compensation expense	30,918	29,684	29,190
Deferred taxes	22,019	(3,878)	(5,815)
Foreign currency transaction losses	3,582	1,276	4,718
Other	(1,620)	7,042	(3,113)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(2,380)	(3,730)	(7,116)
(Increase)/decrease in receivables from broker-dealers, clearing organizations and customers	(123,038)	320,091	(181,044)
Decrease in prepaid expenses and other assets	819	1,009	(11,898)
(Decrease) in accrued employee compensation	3,195	7,049	1,466
Increase/(decrease) in payables to broker-dealers, clearing organizations and customers	99,172	(318,229)	227,920
Increase/(decrease) in income and other tax liabilities	23,510	(3,284)	(14,691)
Increase in accounts payable, accrued expenses and other liabilities	4,000	3,543	(7,229)
(Decrease) in operating lease liabilities	(9,019)	(8,730)	(6,735)
Net cash provided by operating activities	382,139	385,237	333,767
Cash flows from investing activities
Proceeds from maturities and sales	10,570	12,440	4,452
Purchases	(12,968)	(42,810)	(28,818)
Acquisition, net of cash acquired	(36,515)	0	(78,476)
Purchases of furniture, equipment and leasehold improvements	(8,204)	(9,942)	(9,326)
Capitalization of software development costs	(49,810)	(46,623)	(43,122)
Net cash (used in) investing activities	(96,927)	(86,935)	(155,290)
Cash flows from financing activities
Cash dividends on common stock	(115,199)	(112,697)	(109,658)
Exercise of stock options	0	2,988	940
Withholding tax payments on Full Value Awards vesting and stock option exercises	(17,155)	(16,194)	(25,839)
Repurchases of common stock	(420,015)	(75,474)	0
Payment of contingent consideration	0	0	(12,500)
Proceeds from short-term borrowings	220,000	344,925	123,995
Repayments of short-term borrowings	0	(344,925)	(123,995)
Net cash (used in) financing activities	(332,369)	(201,377)	(147,057)
Effect of exchange rate changes on cash and cash equivalents	22,549	(8,138)	7,588
Cash and cash equivalents including restricted cash
Net increase/(decrease) for the period	(24,608)	88,787	39,008
Beginning of period	700,459	611,672	572,664
End of period	675,851	700,459	611,672
Supplemental cash flow information
Cash paid for income taxes	62,834	96,932	94,814
Cash paid for interest	721	1,717	1,870
Non-cash investing and financing activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	783	1,840	1,183
Furniture, equipment, software and leasehold improvement additions included in accounts payable	415	693	0
Stock-based and accrued incentive compensation relating to capitalized software development costs	7,534	5,542	0
Excise tax on repurchases of common stock	3,361	0	0
Exercise of stock options - cashless	0	1,735	0
Fair value of assets acquired	82,568	0	127,635
Cash paid for acquisition, net of cash and cash equivalents acquired	(36,515)	0	(78,476)
Fair value of previously held interest on acquisition date	(33,866)	0	0
Fair value of remaining noncontrolling interests on acquisition date	(10,365)	0	0
Treasury stock used for acquisition	0	0	(43,841)
Liabilities assumed	1,822	0	5,318
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	206	(629)	(25,248)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	$ (359)	$ (621)	$ (1,103)