Consolidated Sponsored Investment Products - Consolidated Statements of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 106,498	$ 100,409	$ 96,140	$ 86,168	$ 78,919	$ 71,951	$ 66,818	$ 62,398	$ 389,215	$ 280,086	$ 204,652
Total operating expenses									275,711	219,641	190,749
Operating income (loss)	33,892	31,630	26,882	21,100	20,472	17,767	14,253	7,953	113,504	60,445	13,903
Total other non-operating income (expense)									8,404	4,358
Income Before Income Taxes									121,908	64,803	12,992
Income tax expense									44,778	27,030	(132,428)
Net income (loss)									77,130	37,773	145,420
Noncontrolling interests									(1,940)	(101)
Allocation of earnings to preferred stockholders										(64)	(24,260)
Net Income Attributable to Common Stockholders	24,756	21,089	15,385	13,960	12,213	11,642	8,367	5,386	75,190	37,608	111,678
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues									389,202	279,919
Total operating expenses									274,913	219,326
Operating income (loss)									114,289	60,593
Total other non-operating income (expense)									5,620	4,106
Income Before Income Taxes									119,909	64,699
Income tax expense									44,778	27,030
Net income (loss)									75,131	37,669
Noncontrolling interests									59	3
Allocation of earnings to preferred stockholders										(64)
Net Income Attributable to Common Stockholders									75,190	37,608
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues
Total operating expenses									785	148
Operating income (loss)									(785)	(148)
Total other non-operating income (expense)									6,098	2,649
Income Before Income Taxes									5,313	2,501
Income tax expense
Net income (loss)									5,313	2,501
Noncontrolling interests
Allocation of earnings to preferred stockholders
Net Income Attributable to Common Stockholders									5,313	2,501
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues									13	167
Total operating expenses									13	167
Operating income (loss)
Total other non-operating income (expense)									(3,314)	(2,397)
Income Before Income Taxes									(3,314)	(2,397)
Income tax expense
Net income (loss)									(3,314)	(2,397)
Noncontrolling interests									(1,999)	(104)
Allocation of earnings to preferred stockholders
Net Income Attributable to Common Stockholders									$ (5,313)	$ (2,501)