Consolidated Sponsored Investment Products - Consolidated Balance Sheets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Total cash	$ 202,847us-gaap_CashEquivalentsAtCarryingValue	$ 271,014us-gaap_CashEquivalentsAtCarryingValue
Total investments	63,448us-gaap_Investments	37,258us-gaap_Investments
All other assets	16,060us-gaap_OtherAssets	15,724us-gaap_OtherAssets
Total assets	698,773us-gaap_Assets	644,954us-gaap_Assets
Total liabilities	112,350us-gaap_Liabilities	109,900us-gaap_Liabilities
Redeemable noncontrolling interest	23,071	42,186
Equity attributable to stockholders of the Company	563,542us-gaap_StockholdersEquity	492,930us-gaap_StockholdersEquity
Non-redeemable noncontrolling interest	(190)us-gaap_MinorityInterest	(62)us-gaap_MinorityInterest
Total liabilities and equity	698,773	644,954
Balances as Reported in Consolidated Balance Sheet [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	211,534	271,545
Total investments	300,100	176,312
All other assets	187,139	197,097
Total assets	698,773	644,954
Total liabilities	112,350	109,900
Redeemable noncontrolling interest	23,071	42,186
Equity attributable to stockholders of the Company	563,542	492,930
Non-redeemable noncontrolling interest	(190)	(62)
Total liabilities and equity	698,773	644,954
Reportable Legal Entities [Member] \| Balance Before Consolidation of Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	202,847	271,014
Total investments	279,863	135,692
All other assets	180,436	187,627
Total assets	663,146	594,333
Total liabilities	99,794	101,465
Redeemable noncontrolling interest	0
Equity attributable to stockholders of the Company	563,542	492,930
Non-redeemable noncontrolling interest	(190)	(62)
Total liabilities and equity	663,146	594,333
Reportable Legal Entities [Member] \| Consolidated Sponsored Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	8,687	531
Total investments	236,652	139,054
All other assets	6,960	9,595
Total assets	252,299	149,180
Total liabilities	12,813	8,560
Redeemable noncontrolling interest	0
Equity attributable to stockholders of the Company	239,486	140,620
Non-redeemable noncontrolling interest	0
Total liabilities and equity	252,299	149,180
Eliminations and Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Total cash	0
Total investments	(216,415)	(98,434)
All other assets	(257)	(125)
Total assets	(216,672)	(98,559)
Total liabilities	(257)	(125)
Redeemable noncontrolling interest	23,071	42,186
Equity attributable to stockholders of the Company	(239,486)	(140,620)
Non-redeemable noncontrolling interest	0
Total liabilities and equity	$ (216,672)	$ (98,559)

Sum of the carrying amounts as of the balance sheet date of all assets that are recognized. Assets are probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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