Consolidated Sponsored Investment Products - Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 107,871	$ 86,168
Total operating expenses	75,245	65,068
Operating income (loss)	32,626	21,100
Total other non-operating income (expense)	3,151	1,535
Income Before Income Taxes	35,777	22,635
Income tax expense	14,010	8,450
Net income (loss)	21,767	14,185
Noncontrolling interests	171	(225)
Net Income Attributable to Common Stockholders	21,938	13,960
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	107,855	86,120
Total operating expenses	74,914	64,884
Operating income (loss)	32,941	21,236
Total other non-operating income (expense)	2,997	1,156
Income Before Income Taxes	35,938	22,392
Income tax expense	14,010	8,450
Net income (loss)	21,928	13,942
Noncontrolling interests	10	18
Net Income Attributable to Common Stockholders	21,938	13,960
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0
Total operating expenses	315	136
Operating income (loss)	(315)	(136)
Total other non-operating income (expense)	910	851
Income Before Income Taxes	595	715
Income tax expense	0
Net income (loss)	595	715
Noncontrolling interests	0
Net Income Attributable to Common Stockholders	595	715
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	16	48
Total operating expenses	16	48
Operating income (loss)	0
Total other non-operating income (expense)	(756)	(472)
Income Before Income Taxes	(756)	(472)
Income tax expense	0
Net income (loss)	(756)	(472)
Noncontrolling interests	161	(243)
Net Income Attributable to Common Stockholders	$ (595)	$ (715)