Consolidated Sponsored Investment Products - Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Total cash	$ 271,014	$ 63,432
Total investments	37,258	18,433
All other assets	15,724	10,950
Total assets	644,954	332,749
Total liabilities	109,900	85,115
Redeemable noncontrolling interest	42,186	3,163
Equity attributable to stockholders of the Company	492,930	244,474	48,270
Non-redeemable noncontrolling interest	(62)	(3)
Total liabilities and equity	644,954	332,749
Balances as Reported in Consolidated Balance Sheet [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	271,545	63,446
Total investments	176,312	61,660
All other assets	197,097	207,643
Total assets	644,954	332,749
Total liabilities	109,900	85,115
Redeemable noncontrolling interest	42,186	3,163
Equity attributable to stockholders of the Company	492,930	244,474
Non-redeemable noncontrolling interest	(62)	(3)
Total liabilities and equity	644,954	332,749
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	271,014	63,432
Total investments	135,692	58,830
All other assets	187,627	206,947
Total assets	594,333	329,209
Total liabilities	101,465	84,738
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	492,930	244,474
Non-redeemable noncontrolling interest	(62)	(3)
Total liabilities and equity	594,333	329,209
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	531	14
Total investments	139,054	43,227
All other assets	9,595	683
Total assets	149,180	43,924
Total liabilities	8,560	364
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	140,620	43,560
Non-redeemable noncontrolling interest
Total liabilities and equity	149,180	43,924
Consolidation, Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash
Total investments	(98,434)	(40,397)
All other assets	(125)	13
Total assets	(98,559)	(40,384)
Total liabilities	(125)	13
Redeemable noncontrolling interest	42,186	3,163
Equity attributable to stockholders of the Company	(140,620)	(43,560)
Non-redeemable noncontrolling interest
Total liabilities and equity	$ (98,559)	$ (40,384)