Parent Company Information - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities
Net Income (Loss)	$ 246,627	$ 274,181	$ 258,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	76,699	73,824	70,557
Amortization of operating lease right-of-use assets	7,523	6,639	5,853
Stock-based compensation expense	30,918	29,684	29,190
Deferred taxes	22,019	(3,878)	(5,815)
Other	(1,620)	7,042	(3,113)
Changes in operating assets and liabilities:
(Increase)/decrease in accounts receivable	(2,380)	(3,730)	(7,116)
Decrease in prepaid expenses and other assets	819	1,009	(11,898)
(Decrease) increase in accrued employee compensation	3,195	7,049	1,466
Increase (decrease) in income and other tax liabilities	23,510	(3,284)	(14,691)
(Decrease)/increase in accounts payable, accrued expenses and other liabilities	4,000	3,543	(7,229)
(Decrease) in operating lease liabilities	(9,019)	(8,730)	(6,735)
Net cash provided by operating activities	382,139	385,237	333,767
Cash flows from investing activities
Acquisition of business	(36,515)	0	(78,476)
Proceeds from maturities and sales	10,570	12,440	4,452
Purchases	(12,968)	(42,810)	(28,818)
Purchases of furniture, equipment and leasehold improvements	(8,204)	(9,942)	(9,326)
Net cash (used in) investing activities	(96,927)	(86,935)	(155,290)
Cash flows from financing activities
Cash dividends on common stock	(115,199)	(112,697)	(109,658)
Exercise of stock options	0	2,988	940
Withholding tax payments on Full Value Awards vesting and stock option exercises	(17,155)	(16,194)	(25,839)
Repurchases of common stock	(420,015)	(75,474)	0
Net cash (used in) financing activities	(332,369)	(201,377)	(147,057)
Effect of exchange rate changes on cash and cash equivalents	22,549	(8,138)	7,588
Cash and cash equivalents including restricted cash
Net increase/(decrease) for the period	(24,608)	88,787	39,008
Beginning of period	700,459	611,672	572,664
End of period	675,851	700,459	611,672
Supplemental cash flow information:
Cash paid for income taxes	62,834	96,932	94,814
Cash paid for interest	721	1,717	1,870
Non-cash investing and financing activity
Excise tax on repurchases of common stock	3,361	0	0
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	783	1,840	1,183
Treasury stock used for acquisition of business	0	0	(43,841)
MarketAxess Holdings Inc. (Parent) [Member]
Cash flows from operating activities
Net Income (Loss)	246,912	274,181	258,055
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,200	2,186	2,153
Amortization of operating lease right-of-use assets	3,986	3,697	3,361
Stock-based compensation expense	7,042	7,130	9,725
Deferred taxes	(625)	397	101
Equity in undistributed income of subsidiaries	(284)	(42,362)	(2,221)
Other	(550)	4,304	(4,675)
Changes in operating assets and liabilities:
(Increase)/decrease in accounts receivable	130	526	(1,154)
Decrease in receivable from subsidiaries	26,332	12,694	5,474
Decrease in prepaid expenses and other assets	2,057	304	1,296
(Decrease) increase in accrued employee compensation	(529)	1,118	(1,104)
(Increase) decrease in income and other tax receivables	(1,526)	(579)	3,800
Increase (decrease) in income and other tax liabilities	(941)	(2,278)	2,287
(Decrease)/increase in accounts payable, accrued expenses and other liabilities	8,495	4,809	(861)
(Decrease) in operating lease liabilities	(5,015)	(4,669)	(3,624)
Net cash provided by operating activities	287,452	261,364	272,424
Cash flows from investing activities
Acquisition of business	(38,069)	0	(81,161)
Investments in subsidiaries	(700)	(30)	(10,058)
Proceeds from maturities and sales	10,570	12,440	4,454
Purchases	(12,968)	(42,810)	(28,818)
Purchases of furniture, equipment and leasehold improvements	(44)	(156)	(239)
Net cash (used in) investing activities	(41,211)	(30,556)	(115,822)
Cash flows from financing activities
Cash dividends on common stock	(115,199)	(112,697)	(109,658)
Exercise of stock options	0	2,988	940
Withholding tax payments on Full Value Awards vesting and stock option exercises	(17,155)	(16,194)	(25,839)
Repurchases of common stock	(420,015)	(75,474)	0
Proceeds from borrowings	220,000	100,000	100,000
Repayments of borrowings	0	(100,000)	(100,000)
Net cash (used in) financing activities	(332,369)	(201,377)	(134,557)
Effect of exchange rate changes on cash and cash equivalents	0	0	(3)
Cash and cash equivalents including restricted cash
Net increase/(decrease) for the period	(86,128)	29,431	22,042
Beginning of period	95,382	65,951	43,909
End of period	9,254	95,382	65,951
Supplemental cash flow information:
Cash paid for income taxes	44,179	53,999	55,784
Cash paid for interest	0	167	35
Non-cash investing and financing activity
Exercise of stock options - cashless	0	1,735	0
Excise tax on repurchases of common stock	3,361	0	0
Operating lease right-of-use assets obtained in exchange for operating lease liabilities	0	0	1,072
Treasury stock used for acquisition of business	0	0	43,841
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	(359)	(621)	(1,103)
Mutual Funds Held In Rabbi Trust [Member] | MarketAxess Holdings Inc. (Parent) [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	(232)	(94)	(189)
Trading Investments [Member]
Changes in operating assets and liabilities:
(Increase)/decrease in trading investments	$ 206	$ (629)	$ (25,248)