Parent Company Information - Condensed Statements of Operations and Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Expenses
Employee compensation and benefits	$ 170,916	$ 156,885	$ 131,079
Depreciation and amortization	53,447	35,996	26,857
Professional and consulting fees	41,925	32,304	25,534
General and administrative	14,501	12,697	15,696
Total expenses	361,716	314,397	260,470
Operating income (loss)	337,235	374,728	250,882
Other income (expense)
Investment income	401	2,446	8,063
Interest expense	(842)	(1,142)
Other, net	(2,871)	(1,673)	(1,521)
Total other income (expense)	(3,312)	(369)	6,542
Benefit from income taxes	76,035	74,982	52,522
Net income	257,888	299,377	204,902
Comprehensive income	249,208	304,997	207,026
MarketAxess Holdings Inc. (Parent) [Member]
Dividends from subsidiaries	173,000	30,000	165,000
Expenses
Employee compensation and benefits	17,887	19,710	16,100
Depreciation and amortization	2,123	2,068	1,919
Professional and consulting fees	7,081	7,332	6,523
General and administrative	3,620	2,723	3,115
Total expenses	30,711	31,833	27,657
Operating income (loss)	142,289	(1,833)	137,343
Other income (expense)
Investment income	132	2,799	5,305
Interest expense		(805)
Other, net	(2,950)	(318)	(1,344)
Total other income (expense)	(2,818)	1,676	3,961
Income (loss) before income taxes and equity in undistributed earnings of subsidiaries	139,471	(157)	141,304
Benefit from income taxes	(6,472)	(23,444)	(9,442)
Income before equity in undistributed income of subsidiaries	145,943	23,287	150,746
Equity in undistributed income of subsidiaries	111,945	276,090	54,156
Net income	257,888	299,377	204,902
Other comprehensive income (loss), net	(8,680)	5,620	2,124
Comprehensive income	$ 249,208	$ 304,997	$ 207,026