Goodwill and Identifiable Intangible Assets (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Goodwill and Identifiable Intangible Assets
Goodwill	$ 138,947	$ 138,947
Accumulated amortization	(31,977)	(31,977)
Total goodwill	106,970	106,970
Mutual fund management advisory contracts	38,699	38,699
Mutual fund management subadvisory contracts	16,300	16,300
Total identifiable intangible assets	54,999	54,999
Total goodwill and identifiable intangible assets	$ 161,969	$ 161,969