Parent Company Information - Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net income	$ 257,888	$ 299,377	$ 204,902
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	53,447	35,996	26,857
Amortization of operating lease right-of-use assets	6,799	6,842	5,795
Stock-based compensation expense	27,314	25,613	25,294
Deferred taxes	3,118	10,099	2,674
Other	(466)	(550)	(778)
Changes in operating assets and liabilities:
Decrease (Increase) in accounts receivable	15,598	(18,015)	(2,962)
Decrease (Increase) in prepaid expenses and other assets	2,214	(1,977)	(4,624)
Increase in accrued employee compensation	(2,607)	14,961	8,312
(Decrease) Increase in income and other tax liabilities	(5,638)	16,189	187
(Decrease) in accounts payable, accrued expenses and other liabilities	215	6,006	(820)
(Decrease) increase in operating lease liabilities	(7,001)	(5,788)	(829)
Net cash provided by operating activities	282,091	404,489	265,935
Cash flows from investing activities
Acquisition of business, net of cash and cash equivalents acquired	0	0	(97,430)
Proceeds from maturities and sales	0	170,657	170,936
Purchases, available-for-sale investments	0	(32,865)	(160,827)
Purchases of furniture, equipment and leasehold improvements	(17,493)	(15,010)	(12,292)
Net cash provided by (used in) investing activities	(67,694)	68,867	(122,051)
Cash flows from financing activities
Cash dividend on common stock	(99,792)	(90,566)	(76,231)
Exercise of stock options	7,096	4,007	1,207
Withholding tax payments on restricted stock vesting and stock option exercises	(33,890)	(42,418)	(25,820)
Repurchases of common stock	(63,189)	(16,135)	(17,256)
Proceeds from short-term borrowings	70,348	578,356	0
Repayments of short-term borrowings	(70,348)	(578,356)	0
Net cash (used in) financing activities	(189,775)	(145,112)	(118,100)
Effect of exchange rate changes on cash and cash equivalents	(7,105)	5,553	1,011
Cash and cash equivalents including restricted cash
Net increase for the period	17,517	333,797	26,795
Beginning of period	608,050	274,253	247,458
End of period	625,567	608,050	274,253
Supplemental cash flow information:
Cash paid for income taxes	70,003	45,046	51,766
Cash paid for interest	830	1,142	0
Non-cash investing and financing activity:
Exercise of stock options - cashless	2,750	10,866	1,811
Treasury stock used for acquisition of business	0	0	(48,830)
MarketAxess Holdings Inc. (Parent) [Member]
Cash flows from operating activities
Net income	257,888	299,377	204,902
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	2,123	2,068	1,919
Amortization of operating lease right-of-use assets	4,484	4,117	4,027
Stock-based compensation expense	12,706	10,834	10,547
Deferred taxes	1,712	3,644	1,255
Equity in undistributed income of subsidiaries	(111,945)	(276,090)	(54,156)
Other	0	(671)	328
Changes in operating assets and liabilities:
Decrease (Increase) in accounts receivable	178	(115)	(4)
Decrease (increase) in receivable from subsidiaries	47,371	25,049	5,253
Decrease (Increase) in prepaid expenses and other assets	(219)	(1,085)	933
Increase in accrued employee compensation	824	3,698	876
Decrease (increase) in income and other tax receivable	7,265	(1,240)	(3,219)
(Decrease) Increase in income and other tax liabilities	(143)	6,676	(2,612)
(Decrease) in accounts payable, accrued expenses and other liabilities	(607)	(442)	(2,039)
(Decrease) increase in operating lease liabilities	(4,673)	(4,055)	1,191
Net cash provided by operating activities	215,449	20,339	168,018
Cash flows from investing activities
Acquisition of business, net of cash and cash equivalents acquired	(17,079)		(102,320)
Proceeds from maturities and sales		170,657	170,936
Purchases, available-for-sale investments		(32,865)	(160,827)
Purchases of furniture, equipment and leasehold improvements	(198)	(337)	(1,424)
Purchase of intangible asset			(30)
Net cash provided by (used in) investing activities	(17,277)	137,455	(93,665)
Cash flows from financing activities
Cash dividend on common stock	(99,791)	(90,566)	(76,231)
Exercise of stock options	7,096	4,007	1,207
Withholding tax payments on restricted stock vesting and stock option exercises	(33,890)	(42,418)	(25,820)
Repurchases of common stock	(63,189)	(16,135)	(17,256)
Proceeds from short-term borrowings		348,000
Repayments of short-term borrowings		(348,000)
Net cash (used in) financing activities	(189,774)	(145,112)	(118,100)
Effect of exchange rate changes on cash and cash equivalents	(2,324)	(5,176)	(3,852)
Cash and cash equivalents including restricted cash
Net increase for the period	6,073	7,506	(47,599)
Beginning of period	55,747	48,241	95,840
End of period	61,820	55,747	48,241
Supplemental cash flow information:
Cash paid for income taxes	41,103	32,674	41,025
Cash paid for interest		805
Non-cash investing and financing activity:
Exercise of stock options - cashless	2,750	10,866	1,811
Treasury stock used for acquisition of business			(48,830)
Mutual Funds Held In Rabbi Trust [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	(2,306)	(2,671)	(2,118)
Mutual Funds Held In Rabbi Trust [Member] | MarketAxess Holdings Inc. (Parent) [Member]
Changes in operating assets and liabilities:
(Increase) decrease in trading investments	$ (1,516)	$ (1,328)	$ (1,183)