Income Taxes - Summary of Company's Net Deferred Tax Assets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred tax assets and liabilities	$ 10,648mktx_DeferredTaxAssetsLiabilitiesGross	$ 12,468mktx_DeferredTaxAssetsLiabilitiesGross
Valuation allowance	(7,371)	(7,428)
Deferred tax assets, net	$ 3,277	$ 5,040

Amount of deferred tax assets for which it is more likely than not that a tax benefit will not be realized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32537-109319

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant