Goodwill and Identifiable Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2015
Goodwill and Identifiable Intangible Assets
Goodwill		$ 106,970	$ 106,970
Mutual fund management advisory contracts		42,753	42,748
Mutual fund management subadvisory contracts		8,400	8,400
Total identifiable intangible assets		51,153	51,148
Total goodwill and identifiable intangible assets		158,123	$ 158,118
Impairment charge	$ 7,900	$ 7,900
Reduction of associated deferred tax liability	2,900
Intangible asset and deferred asset related to the fund adoption transaction agreement with Emerging Managers Group, L.P.	$ 4,100