Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024
Cash flows from operating activities
Net income	$ 154,518	$ 209,042
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	57,093	55,284
Amortization of operating lease right-of-use assets	5,544	5,025
Stock-based compensation expense	23,717	23,065
Deferred taxes	16,159	(1,823)
Foreign currency transaction losses	2,921	5,795
Other	(288)	(2,839)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(11,148)	(11,677)
(Increase)/decrease in receivables from broker-dealers, clearing organizations and customers	(226,736)	208,520
Decrease in prepaid expenses and other assets	4,358	3,203
(Decrease) in accrued employee compensation	(8,841)	(7,795)
Increase/(decrease) in payables to broker-dealers, clearing organizations and customers	139,132	(261,718)
Increase/(decrease) in income and other tax liabilities	82,217	(5,150)
(Decrease) in accounts payable, accrued expenses and other liabilities	(8,557)	(2,085)
(Decrease) in operating lease liabilities	(6,665)	(6,646)
Net cash provided by operating activities	223,507	208,989
Cash flows from investing activities
Proceeds from maturities and sales	8,420	8,995
Purchases	(9,231)	(38,746)
Acquisition, net of cash acquired	(36,515)	0
Purchases of furniture, equipment and leasehold improvements	(4,632)	(9,727)
Capitalization of software development costs	(38,035)	(35,790)
Net cash (used in) investing activities	(79,993)	(75,268)
Cash flows from financing activities
Cash dividends on common stock	(87,151)	(84,999)
Exercise of stock options	0	2,421
Withholding tax payments on Full Value Awards vesting and stock option exercises	(16,761)	(15,263)
Repurchases of common stock	(120,015)	(58,629)
Proceeds from short-term borrowings	0	344,925
Repayments of short-term borrowings	0	(344,925)
Net cash (used in) financing activities	(223,927)	(156,470)
Effect of exchange rate changes on cash and cash equivalents	22,728	11,082
Cash and cash equivalents including restricted cash
Net decrease for the period	(57,685)	(11,667)
Beginning of period	700,459	611,672
End of period	642,774	600,005
Supplemental cash flow information
Cash paid for income taxes	28,764	76,044
Cash paid for interest	541	1,399
Non-cash investing and financing activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	372	1,647
Furniture, equipment, software and leasehold improvement additions included in accounts payable	2,473	646
Stock-based and accrued incentive compensation relating to capitalized software development costs	5,613	3,885
Exercise of stock options - cashless	0	1,735
Fair value of assets acquired	82,568	0
Cash paid for acquisition, net of cash and cash equivalents acquired	(36,515)	0
Fair value of previously held interest on acquisition date	(33,866)	0
Fair value of remaining noncontrolling interests on acquisition date	(10,365)	0
Liabilities assumed	1,822	0
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	198	(629)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	$ (115)	$ (583)