Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Cash flows from operating activities
Net Income (Loss)	$ 137,553	$ 133,487
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	36,556	33,466
Amortization of operating lease right-of-use assets	3,238	2,717
Stock-based compensation expense	15,084	14,378
Deferred taxes	(2,461)	(2,442)
Foreign currency transaction (gains) losses	1,220	3,932
Other	509	(2,641)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(2,882)	(13,078)
Decrease in receivables from broker-dealers, clearing organizations and customers	87,335	19,154
(Increase) in prepaid expenses and other assets	(260)	(12,413)
(Decrease) in accrued employee compensation	(17,843)	(20,746)
(Decrease) in payables to broker-dealers, clearing organizations and customers	(144,404)	(21,749)
Increase in securities sold, not yet purchased	9,167	0
(Decrease) in income and other tax liabilities	(5,197)	(7,720)
Increase/(decrease) in accounts payable, accrued expenses and other liabilities	1,106	(9,762)
(Decrease) in operating lease liabilities	(4,278)	(3,109)
Net cash provided by operating activities	113,900	112,921
Cash flows from investing activities
Proceeds from maturities and sales	7,464	1,971
Purchases	(7,866)	(26,751)
Purchases of furniture, equipment and leasehold improvements	(8,892)	(1,272)
Capitalization of software development costs	(24,459)	(21,715)
Net cash (used in) investing activities	(33,753)	(47,767)
Cash flows from financing activities
Cash dividends on common stock	(57,296)	(55,248)
Exercise of stock options	1,977	725
Withholding tax payments on full value awards vesting and stock option exercises	(15,099)	(20,647)
Repurchases of common stock	(43,597)	0
Payment of contingent consideration	0	(12,500)
Proceeds from short-term borrowings	100,000	50,000
Repayments of short-term borrowings	(100,000)	(50,000)
Net cash (used in) financing activities	(114,015)	(87,670)
Effect of exchange rate changes on cash and cash equivalents	(3,674)	7,181
Cash and cash equivalents including restricted cash
Net decrease for the period	(37,542)	(15,335)
Beginning of period	611,672	572,664
End of period	574,130	557,329
Supplemental cash flow information
Cash paid for income taxes	47,207	63,801
Cash paid for interest	857	241
Non-cash investing and financing activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	760	0
Furniture, equipment, software and leasehold improvement additions included in accounts payable	485	0
Stock-based and accrued incentive compensation relating to capitalized software development costs	2,431	0
Exercise of stock options - cashless	1,735	0
Trading Investments [Member]
Changes in operating assets and liabilities:
Decrease/(increase) in trading investments	155	471
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
Decrease/(increase) in trading investments	$ (698)	$ (1,024)