Goodwill and Other Intangible Assets - Additional Information 1 (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	$ 1,068,506,000	$ 1,068,506,000	$ 1,068,506,000
Other intangible assets, net	802,360,000	841,228,000
Other intangible assets, accumulated amortization	463,400,000	348,566,000
Impairment of non-amortizable intangible asset		98,129,000	19,826,000
Indefinite lived intangible assets excluding goodwill	191,537,000	204,250,000
Amortization expense	138,100,000	85,400,000	78,600,000
Estimated annual amortization expense, 2015	127,900,000
Estimated annual amortization expense, 2016	95,400,000
Estimated annual amortization expense, 2017	85,900,000
Estimated annual amortization expense, 2018	72,700,000
Estimated annual amortization expense, 2019	47,000,000
Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets excluding goodwill	56,800,000	56,800,000
Clarion Partners trade name [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite lived intangible assets excluding goodwill	20,400,000
Trade names [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	18,260,000
Indefinite lived intangible assets excluding goodwill	20,400,000	20,400,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	2 years
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	141,757,000	102,429,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	20 years
Mortgage servicing rights [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	109,856,000	79,448,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	10 years
Management contracts [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	70,312,000	49,785,000
Indefinite lived intangible assets excluding goodwill	114,337,000	127,050,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	13 years
Backlog and incentive fees [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	59,728,000	61,507,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	1 year
Other amortizable intangible assets [Member]
Finite-Lived Intangible Assets [Line Items]
Other intangible assets, accumulated amortization	63,487,000	55,397,000
Amortizable intangible assets, net servicing income expected to received, Maximum, years	20 years
Norland [Member]
Finite-Lived Intangible Assets [Line Items]
Goodwill impairment	0	0	0
Impairment of non-amortizable intangible asset		$ 98,100,000