Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash flows from operating activities
Net income	$ 190,998	$ 205,703
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	45,716	38,840
Amortization of operating lease right-of-use assets	4,232	5,055
Stock-based compensation expense	21,953	20,312
Deferred taxes	(3,346)	3,038
Foreign currency transaction gains	(13,595)	0
Other	730	(46)
Changes in operating assets and liabilities:
(Increase) decrease in accounts receivable	(24,011)	11,820
(Increase) in receivables from broker-dealers, clearing organizations and customers	(148,558)	(288,107)
(Increase) in prepaid expenses and other assets	(4,693)	(1,915)
(Decrease) in accrued employee compensation	(14,502)	(13,280)
Increase in payables to broker-dealers, clearing organizations and customers	107,560	170,113
(Decrease) in income and other tax liabilities	(8,337)	(914)
Increase (decrease) in accounts payable, accrued expenses and other liabilities	2,762	(1,418)
(Decrease) in operating lease liabilities	(4,688)	(5,338)
Net cash provided by operating activities	155,005	136,380
Cash flows from investing activities
Acquisitions, net of cash and cash equivalents acquired	0	(17,078)
Acquisition of equity method investment	(34,400)	0
Purchases of furniture, equipment and leasehold improvements	(6,642)	(14,567)
Capitalization of software development costs	(27,109)	(24,650)
Net cash (used in) provided by investing activities	(68,151)	(56,295)
Cash flows from financing activities
Cash dividend on common stock	(79,855)	(74,999)
Exercise of stock options	284	6,948
Withholding tax payments on restricted stock vesting and stock option exercises	(22,205)	(33,371)
Repurchases of common stock	(87,540)	(18,192)
Payment of contingent consideration	(26,164)	0
Proceeds from short-term borrowings	100,000	70,348
Repayments of short-term borrowings	(100,000)	(70,348)
Net cash (used in) financing activities	(215,480)	(119,614)
Effect of exchange rate changes on cash and cash equivalents	(28,111)	(4,720)
Cash and cash equivalents including restricted cash
Net decrease for the period	(156,737)	(44,249)
Beginning of period	625,567	608,050
End of period	468,830	563,801
Supplemental cash flow information
Cash paid for income taxes	69,085	48,669
Cash paid for interest	658	676
Non-cash activity
Contingent consideration payable recognized in connection with acquisitions	0	26,898
Exercise of stock options - cashless	0	2,750
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,670	1,891
Trading Investments [Member]
Changes in operating assets and liabilities:
Decrease (increase) in trading investments	445	(5,569)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
Decrease (increase) in trading investments	$ 2,339	$ (1,914)