Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Cash flows from operating activities
Net Income (Loss)	$ 133,487	$ 131,691
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	33,466	30,414
Amortization of operating lease right-of-use assets	2,717	2,999
Stock-based compensation expense	14,378	14,602
Deferred taxes	(2,442)	(2,164)
Foreign currency transaction (gains) losses	3,932	0
Other	(2,641)	(1,068)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(13,078)	(23,728)
Decrease (increase) in receivables from broker-dealers, clearing organizations and customers	19,154	(190,074)
(Increase) in prepaid expenses and other assets	(12,413)	(3,632)
(Decrease) in accrued employee compensation	(20,746)	(24,034)
(Decrease) increase in payables to broker-dealers, clearing organizations and customers	(21,749)	145,886
(Decrease) in income and other tax liabilities	(7,720)	(10,175)
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(9,762)	1,141
(Decrease) in operating lease liabilities	(3,109)	(3,287)
Net cash provided by operating activities	112,921	69,907
Cash flows from investing activities
Proceeds from maturities and sales	1,971	0
Purchases	(26,751)	0
Acquisition of equity method investment	0	(34,400)
Purchases of furniture, equipment and leasehold improvements	(1,272)	(2,681)
Capitalization of software development costs	(21,715)	(18,561)
Net cash (used in) investing activities	(47,767)	(55,642)
Cash flows from financing activities
Cash dividend on common stock	(55,248)	(53,527)
Exercise of stock options	725	136
Withholding tax payments on restricted stock vesting and stock option exercises	(20,647)	(19,953)
Repurchases of common stock	0	(87,540)
Payment of contingent consideration	(12,500)	(26,164)
Proceeds from short-term borrowings	50,000	100,000
Repayments of short-term borrowings	(50,000)	(100,000)
Net cash (used in) financing activities	(87,670)	(187,048)
Effect of exchange rate changes on cash and cash equivalents	7,181	(23,894)
Cash and cash equivalents including restricted cash
Net decrease for the period	(15,335)	(196,677)
Beginning of period	572,664	625,567
End of period	557,329	428,890
Supplemental cash flow information
Cash paid for income taxes	63,801	47,991
Cash paid for interest	241	429
Non-cash activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	0	1,651
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	(471)	0
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	$ (1,024)	$ 1,336