Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2026	Jun. 30, 2025
Cash flows from operating activities
Net income	$ 146,430	$ 86,245
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	38,519	37,431
Amortization of operating lease right-of-use assets	3,906	3,626
Stock-based compensation expense	17,830	15,345
Deferred taxes	(638)	(706)
Foreign currency transaction losses	(634)	4,080
Other	5,278	(2,826)
Changes in operating assets and liabilities:
(Increase) in accounts receivable	(34,527)	(13,146)
(Increase) in receivables from broker-dealers, clearing organizations and customers	(728,239)	(159,675)
(Increase)/decrease in prepaid expenses and other assets	(1,821)	2,826
(Decrease) in accrued employee compensation	(24,296)	(19,696)
Increase in payables to broker-dealers, clearing organizations and customers	541,224	99,968
(Decrease)/increase in income and other tax liabilities	(7,961)	91,406
Increase/(decrease) in accounts payable, accrued expenses and other liabilities	1,600	(6,913)
(Decrease) in operating lease liabilities	(4,608)	(4,373)
Net cash (used in)/provided by operating activities	(48,517)	133,343
Cash flows from investing activities
Proceeds from maturities and sales	6,891	7,246
Purchases	(8,286)	(9,231)
Acquisition, net of cash acquired	0	(36,515)
Purchases of furniture, equipment and leasehold improvements	(908)	(3,136)
Capitalization of software development costs	(28,449)	(26,541)
Net cash (used in) investing activities	(30,752)	(68,177)
Cash flows from financing activities
Payment of the excise tax on repurchases	(3,361)	0
Cash dividends on common stock	(55,890)	(57,705)
Withholding tax payments on Full Value Awards vesting and stock option exercises	(8,935)	(9,846)
Repurchases of common stock	0	(74,764)
Proceeds from borrowings	130,164	0
Repayments of borrowings	(234,250)	0
Net cash (used in) financing activities	(172,272)	(142,315)
Effect of exchange rate changes on cash and cash equivalents	(4,589)	27,144
Net decrease for the period	(256,130)	(50,005)
Beginning of period	675,851	700,459
End of period	419,721	650,454
Supplemental cash flow information
Cash paid/(refunded) for income taxes	51,555	9,852
Cash paid for interest	4,865	342
Non-cash investing and financing activity
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	2,904	407
Fair value of assets acquired	0	86,413
Cash paid for acquisition, net of cash and cash equivalents acquired	0	(36,515)
Fair value of previously held interest on acquisition date	0	(34,321)
Fair value of remaining noncontrolling interests on acquisition date	0	(13,755)
Liabilities assumed	0	1,822
Software development costs [Member]
Non-cash investing and financing activity
Stock-based and accrued incentive compensation relating to capitalized software development costs	3,980	3,633
Furniture, equipment, software and leasehold improvement [Member]
Non-cash investing and financing activity
Furniture, equipment, software and leasehold improvement additions included in accounts payable	563	664
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	0	(66)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	$ (580)	$ (183)