Parent Company Information - Condensed Statements of Financial Condition (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
ASSETS
Cash and cash equivalents	$ 270,124	$ 246,322
Investments, at fair value	230,477	240,105
Accounts receivable	62,017	57,535
Intangible assets, net of accumulated amortization	60,986	2,962
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	71,795	63,010
Operating lease right-of-use assets	81,399
Prepaid expenses and other assets	30,770	22,468
Deferred tax assets, net	501	3,424
Total assets	954,930	695,539
Liabilities
Accrued employee compensation	47,365	39,053
Income and other tax liabilities	16,690	16,432
Accounts payable, accrued expenses and other liabilities	19,294	29,366
Operating lease liabilities	97,991
Total liabilities	184,839	87,661
Stockholders' equity
Preferred stock
Common stock	122	122
Additional paid-in capital	342,541	341,860
Treasury stock	(153,388)	(184,962)
Retained earnings	591,086	463,252
Accumulated other comprehensive loss	(10,270)	(12,394)
Total stockholders' equity	770,091	607,878	$ 514,768	$ 468,013
Total liabilities and stockholders' equity	954,930	695,539
Series A Preferred Stock [Member]
Stockholders' equity
Preferred stock
MarketAxess Holdings Inc. (Parent) [Member]
ASSETS
Cash and cash equivalents	48,241	95,840
Investments, at fair value	141,318	149,266
Accounts receivable	63	59
Receivable from subsidiaries	5,997
Intangible assets, net of accumulated amortization	30
Furniture, equipment, leasehold improvements and capitalized software, net of accumulated depreciation and amortization	25,247	25,742
Operating lease right-of-use assets	68,559
Investments in subsidiaries	570,145	356,363
Prepaid expenses and other assets	3,506	4,439
Deferred tax assets, net	3,472	5,039
Income and other tax receivable	3,219
Total assets	869,797	636,748
Liabilities
Accrued employee compensation	6,543	5,667
Income and other tax liabilities		2,612
Payable to subsidiaries		3
Accounts payable, accrued expenses and other liabilities	9,254	20,588
Operating lease liabilities	83,909
Total liabilities	99,706	28,870
Stockholders' equity
Preferred stock
Common stock	122	122
Additional paid-in capital	342,541	341,860
Treasury stock	(153,388)	(184,962)
Retained earnings	591,086	463,252
Accumulated other comprehensive loss	(10,270)	(12,394)
Total stockholders' equity	770,091	607,878
Total liabilities and stockholders' equity	869,797	636,748
MarketAxess Holdings Inc. (Parent) [Member] | Series A Preferred Stock [Member]
Stockholders' equity
Preferred stock