Consolidated Sponsored Investment Products - Condensed Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Total cash	$ 170,367	$ 271,014
Total investments	65,099	37,258
All other assets	15,584	15,724
Total assets	640,679	644,954
Total liabilities	115,855	109,900
Redeemable noncontrolling interests	10,397	42,186
Equity attributable to stockholders of the Company	514,529	492,930
Non-redeemable noncontrolling interests	(102)	(62)
Total liabilities and equity	640,679	644,954
Balances as Reported in Consolidated Balance Sheet [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	182,686	271,545
Total investments	272,378	176,312
All other assets	185,615	197,097
Total assets	640,679	644,954
Total liabilities	115,855	109,900
Redeemable noncontrolling interests	10,397	42,186
Equity attributable to stockholders of the Company	514,529	492,930
Non-redeemable noncontrolling interests	(102)	(62)
Total liabilities and equity	640,679	644,954
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	170,367	271,014
Total investments	261,414	135,692
All other assets	182,490	187,627
Total assets	614,271	594,333
Total liabilities	99,844	101,465
Redeemable noncontrolling interests	0
Equity attributable to stockholders of the Company	514,529	492,930
Non-redeemable noncontrolling interests	(102)	(62)
Total liabilities and equity	614,271	594,333
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	12,319	531
Total investments	207,279	139,054
All other assets	3,285	9,595
Total assets	222,883	149,180
Total liabilities	16,171	8,560
Redeemable noncontrolling interests	0
Equity attributable to stockholders of the Company	206,712	140,620
Non-redeemable noncontrolling interests	0
Total liabilities and equity	222,883	149,180
Eliminations and Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	0
Total investments	(196,315)	(98,434)
All other assets	(160)	(125)
Total assets	(196,475)	(98,559)
Total liabilities	(160)	(125)
Redeemable noncontrolling interests	10,397	42,186
Equity attributable to stockholders of the Company	(206,712)	(140,620)
Non-redeemable noncontrolling interests	0
Total liabilities and equity	$ (196,475)	$ (98,559)