Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Cash flows from operating activities
Net income	$ 73,628	$ 64,769
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	16,461	15,174
Amortization of operating lease right-of-use assets	1,368	1,596
Stock-based compensation expense	7,488	8,099
Deferred taxes	(1,433)	(643)
Foreign currency transaction (gains) losses	1,699	0
Other	(2,532)	(1,229)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(21,935)	(11,699)
(Increase) in receivables from broker-dealers, clearing organizations and customers	(52,549)	(296,015)
Decrease (increase) in prepaid expenses and other assets	3,163	(2,445)
(Decrease) in accrued employee compensation	(31,567)	(33,553)
Increase in payables to broker-dealers, clearing organizations and customers	12,281	229,151
Increase in income and other tax liabilities	10,904	3,049
(Decrease) increase in accounts payable, accrued expenses and other liabilities	(6,838)	1,932
(Decrease) in operating lease liabilities	(1,562)	(1,799)
Net cash provided by (used in) operating activities	7,527	(23,730)
Cash flows from investing activities
Proceeds from maturities and sales	1,048	0
Purchases	(22,895)	0
Purchases of furniture, equipment and leasehold improvements	(217)	(1,396)
Capitalization of software development costs	(10,690)	(9,425)
Net cash (used in) investing activities	(32,754)	(10,821)
Cash flows from financing activities
Cash dividend on common stock	(28,357)	(27,425)
Exercise of stock options	707	50
Withholding tax payments on restricted stock vesting and stock option exercises	(20,492)	(20,292)
Repurchases of common stock	0	(38,800)
Proceeds from short-term borrowings	50,000	100,000
Repayments of short-term borrowings	(50,000)	(100,000)
Net cash (used in) financing activities	(48,142)	(86,467)
Effect of exchange rate changes on cash and cash equivalents	3,345	(4,356)
Cash and cash equivalents including restricted cash
Net decrease for the period	(70,024)	(125,374)
Beginning of period	572,664	625,567
End of period	502,640	500,193
Supplemental cash flow information
Cash paid for income taxes	11,660	8,487
Cash paid for interest	187	134
Non-cash activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	0	91
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase) in trading investments	(419)	0
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) in trading investments	$ (630)	$ (117)