Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities
Net Income (Loss)	$ 188,428	$ 190,998
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	51,027	45,716
Amortization of operating lease right-of-use assets	4,207	4,232
Stock-based compensation expense	21,859	21,953
Deferred taxes	(5,502)	(3,346)
Foreign currency transaction (gains) losses	1,587	(13,595)
Other	847	730
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(11,650)	(24,011)
(Increase) in receivables from broker-dealers, clearing organizations and customers	(46,146)	(148,558)
(Increase) in prepaid expenses and other assets	(18,240)	(4,693)
(Decrease) in accrued employee compensation	(12,406)	(14,502)
Increase in payables to broker-dealers, clearing organizations and customers	58,710	107,560
(Decrease) in income and other tax liabilities	(3,921)	(8,337)
(Decrease)/increase in accounts payable, accrued expenses and other liabilities	(7,491)	2,762
(Decrease) in operating lease liabilities	(4,721)	(4,688)
Net cash provided by operating activities	192,082	155,005
Cash flows from investing activities
Proceeds from maturities and sales	3,311	0
Purchases	(27,871)	0
Acquisition of equity method investment	0	(34,400)
Purchases of furniture, equipment and leasehold improvements	(7,255)	(6,642)
Capitalization of software development costs	(31,802)	(27,109)
Net cash (used in) investing activities	(63,617)	(68,151)
Cash flows from financing activities
Cash dividend on common stock	(82,139)	(79,855)
Exercise of stock options	725	284
Withholding tax payments on restricted stock vesting and stock option exercises	(20,863)	(22,205)
Repurchases of common stock	0	(87,540)
Payment of contingent consideration	(12,500)	(26,164)
Proceeds from short-term borrowings	53,995	100,000
Repayments of short-term borrowings	(50,000)	(100,000)
Net cash (used in) financing activities	(110,782)	(215,480)
Effect of exchange rate changes on cash and cash equivalents	(1,451)	(28,111)
Cash and cash equivalents including restricted cash
Net increase (decrease) for the period	16,232	(156,737)
Beginning of period	572,664	625,567
End of period	588,896	468,830
Supplemental cash flow information
Cash paid for income taxes	83,142	69,085
Cash paid for interest	396	658
Non-cash activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,178	1,670
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	(24,300)	445
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	$ (206)	$ 2,339