Net Capital Requirements and Customer Protection Requirements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Net capital requirements and customer protection requirements
Minimum net capital required	$ (100)
MarketAxess Corporation [Member]
Net capital requirements and customer protection requirements
Net capital	75,058
Minimum net capital required	2,544
Excess net capital	72,514
MarketAxess Europe Limited [Member]
Net capital requirements and customer protection requirements
Net capital	13,078
Minimum net capital required	2,927
Excess net capital	10,151
MarketAxess Canada Limited [Member]
Net capital requirements and customer protection requirements
Net capital	431
Minimum net capital required	280
Excess net capital	$ 151