Goodwill And Other Intangible Assets (Narrative) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009	Dec. 31, 2008
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Stock price per share				$ 18.65	$ 13.46	$ 18.13	$ 10.94	$ 4.32
Other intangible assets, net	$ 786,793,000	$ 794,325,000
Other intangible assets, accumulated amortization	273,631,000	194,982,000
Unamortizable intangible assets, identified as a result of acquisition	296,332,000	313,041,000
Amortization expense	78,600,000	41,900,000	23,100,000
Estimated annual amortization expense, 2013	71,800,000
Estimated annual amortization expense, 2014	61,000,000
Estimated annual amortization expense, 2015	56,200,000
Estimated annual amortization expense, 2016	48,000,000
Estimated annual amortization expense, 2017	44,000,000
Customer Relationships [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	84,628,000	66,994,000
Amortizable intangible assets, useful life, Maximum, years	20 years
Management Contracts [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	32,005,000	14,667,000
Unamortizable intangible assets, identified as a result of acquisition	219,132,000	216,015,000
Amortizable intangible assets, useful life, Maximum, years	13 years
Mortgage Servicing Rights [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	50,858,000	33,560,000
Amortizable intangible assets, useful life, Maximum, years	10 years
Backlog And Incentive Fees [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	57,739,000	47,237,000
Amortizable intangible assets, useful life, Maximum, years	1 year
Other Amortizable Intangible Assets [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	48,401,000	32,524,000
Amortizable intangible assets, useful life, Maximum, years	20 years
Trademarks [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Unamortizable intangible assets, identified as a result of acquisition	56,800,000	56,800,000
Clarion Partners Trade Name [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Unamortizable intangible assets, identified as a result of acquisition	20,400,000
Trade Names [Member]
Schedule Of Goodwill And Other Intangible Assets [Line Items]
Unamortizable intangible assets, identified as a result of acquisition	$ 20,400,000	$ 40,226,000