Parent Company Information - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Revenues	$ 817,097	$ 752,547	$ 718,300
Expenses
Employee compensation and benefits	235,880	206,926	182,104
Depreciation and amortization	73,824	70,557	61,446
Technology and communications	72,166	62,801	52,964
Professional and consulting fees	27,382	31,935	33,949
Occupancy	14,690	14,216	14,121
General and administrative	22,709	23,042	19,200
Total expenses	476,227	437,528	391,424
Operating income	340,870	315,019	326,876
Other income (expense)
Interest expense	1,601	1,983	700
Equity in earnings of unconsolidated affiliate	1,395	735	1,126
Other, net	(6,164)	(3,496)	5,946
Total other income (expense)	19,676	17,681	11,412
Income before income taxes and equity in undistributed earnings of subsidiaries	360,546	332,700	338,288
Benefit from income taxes	86,365	74,645	88,064
Net income	274,181	258,055	250,224
Comprehensive income	263,852	271,382	225,857
MarketAxess Holdings Inc. (Parent) [Member]
Revenues	246,600	270,700	257,200
Expenses
Employee compensation and benefits	12,091	13,938	17,655
Depreciation and amortization	2,186	2,153	2,136
Professional and consulting fees	6,149	5,828	5,528
General and administrative	1,660	2,301	3,081
Total expenses	22,086	24,220	28,400
Operating income	224,514	246,480	228,800
Other income (expense)
Interest income	4,615	3,557	272
Interest expense	(167)	(155)	(271)
Equity in earnings of unconsolidated affiliate	1,395	735	1,126
Other, net	(5,088)	(369)	(2,633)
Total other income (expense)	755	3,768	(1,506)
Income before income taxes and equity in undistributed earnings of subsidiaries	225,269	250,248	227,294
Benefit from income taxes	(6,550)	(5,586)	(7,710)
Income before equity in undistributed income of subsidiaries	231,819	255,834	235,004
Equity in undistributed income of subsidiaries	42,362	2,221	15,220
Net income	274,181	258,055	250,224
Other comprehensive income (loss), net	(10,329)	13,327	(24,367)
Comprehensive income	$ 263,852	$ 271,382	$ 225,857