Parent Company Information - Condensed Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
ASSETS
Cash and cash equivalents	$ 519,734	$ 544,478
Investments, at fair value	170,677	165,260
Accounts receivable	100,989	91,845
Intangible assets, net of accumulated amortization	110,629	98,078
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	112,431	107,298
Operating lease right-of-use assets	51,854	58,132
Prepaid expenses and other assets	46,972	82,584
Total assets	1,934,886	1,789,216
Liabilities
Accrued employee compensation	73,879	68,054
Income and other tax liabilities	49,267	3,683
Borrowings	220,000	0
Accounts payable, accrued expenses and other liabilities	42,584	37,320
Operating lease liabilities	64,938	72,654
Total liabilities	776,627	400,556
Redeemable noncontrolling interest	12,592	0
Stockholders' equity
Preferred stock	0	0
Common stock voting	123	123
Additional paid-in capital	305,923	350,701
Treasury stock	(694,764)	(333,369)
Retained earnings	1,538,746	1,405,904
Accumulated other comprehensive loss	(4,361)	(34,699)
Total stockholders' equity	1,145,667	1,388,660	$ 1,292,963	$ 1,081,093
Total liabilities, redeemable noncontrolling interest and stockholders' equity	1,934,886	1,789,216
MarketAxess Holdings Inc. (Parent) [Member]
ASSETS
Cash and cash equivalents	9,254	94,332
Investments, at fair value	64,298	60,735
Accounts receivable	1,267	1,397
Receivable from subsidiaries	13,754	22,606
Intangible assets, net of accumulated amortization	16	18
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	13,464	15,617
Operating lease right-of-use assets	47,430	51,416
Investments in subsidiaries	1,300,111	1,179,524
Prepaid expenses and other assets	7,294	40,903
Income and other tax receivable	9,779	8,253
Total assets	1,466,667	1,474,801
Liabilities
Accrued employee compensation	9,178	9,707
Income and other tax liabilities	3,142	722
Borrowings	220,000	0
Accounts payable, accrued expenses and other liabilities	16,037	10,646
Operating lease liabilities	60,051	65,066
Total liabilities	308,408	86,141
Redeemable noncontrolling interest	12,592	0
Stockholders' equity
Preferred stock	0	0
Common stock voting	123	123
Additional paid-in capital	305,923	350,701
Treasury stock	(694,764)	(333,369)
Retained earnings	1,538,746	1,405,904
Accumulated other comprehensive loss	(4,361)	(34,699)
Total stockholders' equity	1,145,667	1,388,660
Total liabilities, redeemable noncontrolling interest and stockholders' equity	1,466,667	1,474,801
Series A Preferred Stock [Member]
Stockholders' equity
Preferred stock	0	0
Series A Preferred Stock [Member] | MarketAxess Holdings Inc. (Parent) [Member]
Stockholders' equity
Preferred stock	$ 0	$ 0