Consolidated Sponsored Investment Products - Condensed Consolidated Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 112,749	$ 96,140	$ 220,620	$ 182,308
Total operating expenses	90,247	69,258	165,492	134,326
Operating income (loss)	22,502	26,882	55,128	47,982
Total other non-operating income (expense)	9,396	(2,781)	12,547	(1,246)
Income Before Income Taxes	31,898	24,101	67,675	46,736
Income tax expense	12,106	9,318	26,116	17,768
Net income (loss)	19,792	14,783	41,559	28,968
Noncontrolling interests	(249)	602	(78)	377
Net income (loss) attributable to the Company	19,543	15,385	41,481	29,345
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	112,871	96,135	220,726	182,256
Total operating expenses	89,450	69,125	164,364	134,010
Operating income (loss)	23,421	27,010	56,362	48,246
Total other non-operating income (expense)	8,198	(2,321)	11,195	(1,165)
Income Before Income Taxes	31,619	24,689	67,557	47,081
Income tax expense	12,106	9,318	26,116	17,768
Net income (loss)	19,513	15,371	41,441	29,313
Noncontrolling interests	30	14	40	32
Net income (loss) attributable to the Company	19,543	15,385	41,481	29,345
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0		0
Total operating expenses	919	128	1,234	264
Operating income (loss)	(919)	(128)	(1,234)	(264)
Total other non-operating income (expense)	8,082	(2,543)	8,992	(1,691)
Income Before Income Taxes	7,163	(2,671)	7,758	(1,955)
Income tax expense	0		0
Net income (loss)	7,163	(2,671)	7,758	(1,955)
Noncontrolling interests	0		0
Net income (loss) attributable to the Company	7,163	(2,671)	7,758	(1,955)
Eliminations and Adjustments [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	(122)	5	(106)	52
Total operating expenses	(122)	5	(106)	52
Operating income (loss)	0		0
Total other non-operating income (expense)	(6,884)	2,083	(7,640)	1,610
Income Before Income Taxes	(6,884)	2,083	(7,640)	1,610
Income tax expense	0		0
Net income (loss)	(6,884)	2,083	(7,640)	1,610
Noncontrolling interests	(279)	588	(118)	345
Net income (loss) attributable to the Company	$ (7,163)	$ 2,671	$ (7,758)	$ 1,955