Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities
Net income	$ 131,691	$ 147,745
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	30,414	24,876
Amortization of operating lease right-of-use assets	2,999	3,368
Stock-based compensation expense	14,602	13,558
Deferred taxes	(2,164)	1,600
Other	(1,068)	(176)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(23,728)	(7,434)
(Increase) in receivables from broker-dealers, clearing organizations and customers	(190,074)	(211,434)
(Increase) in prepaid expenses and other assets	(3,632)	(4,624)
(Decrease) in accrued employee compensation	(24,034)	(23,048)
Increase in payables to broker-dealers, clearing organizations and customers	145,886	144,977
(Decrease) in income and other tax liabilities	(10,175)	(3,101)
Increase (decrease) in accounts payable, accrued expenses and other liabilities	1,141	(1,479)
(Decrease) in operating lease liabilities	(3,287)	(3,732)
Net cash provided by operating activities	69,907	73,567
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	(2,681)	(9,809)
Capitalization of software development costs	(18,561)	(16,459)
Net cash (used in) provided by investing activities	(55,642)	(43,346)
Cash flows from financing activities
Cash dividend on common stock	(53,527)	(50,238)
Exercise of stock options	136	4,665
Withholding tax payments on restricted stock vesting and stock option exercises	(19,953)	(34,282)
Repurchases of common stock	(87,540)	(13,956)
Payment of contingent consideration	(26,164)	0
Proceeds from short-term borrowings	100,000	70,348
Repayments of short-term borrowings	(100,000)	(69,302)
Net cash (used in) financing activities	(187,048)	(92,765)
Effect of exchange rate changes on cash and cash equivalents	(23,894)	(263)
Cash and cash equivalents including restricted cash
Net decrease for the period	(196,677)	(62,807)
Beginning of period	625,567	608,050
End of period	428,890	545,243
Supplemental cash flow information
Cash paid for income taxes	47,991	36,798
Cash paid for interest	429	362
Non-cash activity
Contingent consideration payable recognized in connection with acquisitions	0	22,450
Exercise of stock options - cashless	0	2,750
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	1,651	1,208
Trading Investments [Member]
Changes in operating assets and liabilities:
Decrease (increase) in trading investments	0	5,569
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
Decrease (increase) in trading investments	$ 1,336	$ (1,960)