Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities
Net Income (Loss)	$ 209,042	$ 188,428
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	55,284	51,027
Amortization of operating lease right-of-use assets	5,025	4,207
Stock-based compensation expense	23,065	21,859
Deferred taxes	(1,823)	(5,502)
Foreign currency transaction losses	5,795	1,587
Other	(2,839)	847
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(11,677)	(11,650)
Decrease/(increase) in receivables from broker-dealers, clearing organizations and customers	208,520	(46,146)
Decrease/(increase) in prepaid expenses and other assets	3,203	(18,240)
(Decrease) in accrued employee compensation	(7,795)	(12,406)
(Decrease)/increase in payables to broker-dealers, clearing organizations and customers	(261,718)	58,710
(Decrease) in income and other tax liabilities	(5,150)	(3,921)
(Decrease) in accounts payable, accrued expenses and other liabilities	(2,085)	(7,491)
(Decrease) in operating lease liabilities	(6,646)	(4,721)
Net cash provided by operating activities	208,989	192,082
Cash flows from investing activities
Proceeds from maturities and sales	8,995	3,311
Purchases	(38,746)	(27,871)
Purchases of furniture, equipment and leasehold improvements	(9,727)	(7,255)
Capitalization of software development costs	(35,790)	(31,802)
Net cash (used in) investing activities	(75,268)	(63,617)
Cash flows from financing activities
Cash dividends on common stock	(84,999)	(82,139)
Exercise of stock options	2,421	725
Withholding tax payments on full value awards vesting and stock option exercises	(15,263)	(20,863)
Repurchases of common stock	(58,629)	0
Payment of contingent consideration	0	(12,500)
Proceeds from short-term borrowings	344,925	53,995
Repayments of short-term borrowings	(344,925)	(50,000)
Net cash (used in) financing activities	(156,470)	(110,782)
Effect of exchange rate changes on cash and cash equivalents	11,082	(1,451)
Cash and cash equivalents including restricted cash
Net increase for the period	(11,667)	16,232
Beginning of period	611,672	572,664
End of period	600,005	588,896
Supplemental cash flow information
Cash paid for income taxes	76,044	83,142
Cash paid for interest	1,399	396
Non-cash investing and financing activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,647	1,178
Furniture, equipment, software and leasehold improvement additions included in accounts payable	646	0
Stock-based and accrued incentive compensation relating to capitalized software development costs	3,885	0
Exercise of stock options - cashless	1,735	0
Trading Investments [Member]
Changes in operating assets and liabilities:
Decrease/(increase) in trading investments	(629)	(24,300)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
Decrease/(increase) in trading investments	$ (583)	$ (206)