Goodwill and Other Intangibles - Other Intangible (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015	May 27, 2016
Other Intangible Assets
Gross Carrying Amount	$ 43,314		$ 43,314		$ 55,814
Accumulated Amortization	26,563		26,563		31,203
Other intangible assets not subject to amortization	8,900		8,900
Amortization expense of other intangible assets	500	$ 800	1,200	$ 1,600
Impairment of other intangible assets			0
Trade name
Other Intangible Assets
Gross Carrying Amount	8,545		8,545		8,545
Trading rights
Other Intangible Assets
Gross Carrying Amount	339		339		339
Other
Other Intangible Assets
Gross Carrying Amount	50		50		50
POSIT trade name
Other Intangible Assets
Other intangible assets not subject to amortization	8,400		8,400
Customer related intangibles
Other Intangible Assets
Gross Carrying Amount	10,822		10,822		23,322
Accumulated Amortization	5,338		5,338		$ 10,400
Useful Lives					14 years 3 months 18 days
Proprietary software
Other Intangible Assets
Gross Carrying Amount	23,558		23,558		$ 23,558
Accumulated Amortization	$ 21,225		$ 21,225		$ 20,803
Useful Lives					6 years 3 months 18 days
Sale of subsidiaries | ITG Investment Research
Other Intangible Assets
Net of accumulated amortization						$ 6,700