Goodwill and Identifiable Intangible Assets (Details) (USD $)	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2012	Dec. 31, 2013	Sep. 30, 2012
Goodwill and Identifiable Intangible Assets
Goodwill		$ 106,970,000		$ 106,970,000
Mutual fund management advisory contracts		42,753,000		38,699,000
Mutual fund management subadvisory contracts		8,400,000		16,300,000
Total identifiable intangible assets		51,153,000		54,999,000
Total goodwill and identifiable intangible assets		158,123,000		161,969,000
Deferred tax liability		12,562,000		16,697,000
Impairment charge	7,900,000	7,900,000
Reduction of associated deferred tax liability	2,900,000
Intangible asset related to the fund adoption transaction agreement with Emerging Managers Group, L.P.	4,100,000
Legend subsidiary
Goodwill, annual impairment test
Goodwill					59,200,000
Impairment charges			$ 42,400,000