Consolidated Sponsored Investment Products - Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Total cash	$ 234,795	$ 271,014
Total investments	102,490	37,258
All other assets	16,104	15,724
Total assets	585,827	644,954
Total liabilities	71,864	109,900
Redeemable noncontrolling interests	3,867	42,186
Equity attributable to stockholders of the Company	510,168	492,930
Non-redeemable noncontrolling interests	(72)	(62)
Total liabilities and equity	585,827	644,954
Balances as Reported in Consolidated Balance Sheet [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	237,338	271,545
Total investments	164,576	176,312
All other assets	183,913	197,097
Total assets	585,827	644,954
Total liabilities	71,864	109,900
Redeemable noncontrolling interests	3,867	42,186
Equity attributable to stockholders of the Company	510,168	492,930
Non-redeemable noncontrolling interests	(72)	(62)
Total liabilities and equity	585,827	644,954
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	234,795	271,014
Total investments	161,910	135,692
All other assets	182,755	187,627
Total assets	579,460	594,333
Total liabilities	69,364	101,465
Redeemable noncontrolling interests	0
Equity attributable to stockholders of the Company	510,168	492,930
Non-redeemable noncontrolling interests	(72)	(62)
Total liabilities and equity	579,460	594,333
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	2,543	531
Total investments	62,086	139,054
All other assets	1,217	9,595
Total assets	65,846	149,180
Total liabilities	2,559	8,560
Redeemable noncontrolling interests	0
Equity attributable to stockholders of the Company	63,287	140,620
Non-redeemable noncontrolling interests	0
Total liabilities and equity	65,846	149,180
Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	0
Total investments	(59,420)	(98,434)
All other assets	(59)	(125)
Total assets	(59,479)	(98,559)
Total liabilities	(59)	(125)
Redeemable noncontrolling interests	3,867	42,186
Equity attributable to stockholders of the Company	(63,287)	(140,620)
Non-redeemable noncontrolling interests	0
Total liabilities and equity	$ (59,479)	$ (98,559)