Parent Company Information - Condensed Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues	$ 846,268	$ 817,097	$ 752,547
Expenses
Employee compensation and benefits	248,537	235,880	206,926
Depreciation and amortization	76,699	73,824	70,557
Professional and consulting fees	31,487	27,382	31,935
General and administrative	26,588	22,709	23,042
Total expenses	504,430	476,227	437,528
Operating income	341,838	340,870	315,019
Other income (expense)
Interest expense	(1,487)	(1,601)	(1,983)
Equity in earnings of unconsolidated affiliate	457	1,395	735
Other, net	1,790	(6,164)	(3,496)
Total other income (expense)	25,157	19,676	17,681
Income before income taxes and equity in undistributed earnings of subsidiaries	366,995	360,546	332,700
Benefit from income taxes	120,083	86,365	74,645
Net income	246,627	274,181	258,055
Comprehensive income available for common stockholders	276,895	263,852	271,382
MarketAxess Holdings Inc. (Parent) [Member]
Revenues	258,450	246,600	270,700
Expenses
Employee compensation and benefits	10,388	12,091	13,938
Depreciation and amortization	2,200	2,186	2,153
Professional and consulting fees	6,341	6,149	5,828
General and administrative	4,154	1,660	2,301
Total expenses	23,083	22,086	24,220
Operating income	235,367	224,514	246,480
Other income (expense)
Interest income	5,202	4,615	3,557
Interest expense	(769)	(167)	(155)
Equity in earnings of unconsolidated affiliate	457	1,395	735
Other, net	2,249	(5,088)	(369)
Total other income (expense)	7,139	755	3,768
Income before income taxes and equity in undistributed earnings of subsidiaries	242,506	225,269	250,248
Benefit from income taxes	(4,122)	(6,550)	(5,586)
Income before equity in undistributed income of subsidiaries	246,628	231,819	255,834
Equity in undistributed income of subsidiaries	284	42,362	2,221
Net income	246,912	274,181	258,055
Other comprehensive income (loss), net	30,338	(10,329)	13,327
Comprehensive income available for common stockholders	$ 277,250	$ 263,852	$ 271,382