Consolidated Sponsored Investment Products - Condensed Consolidated Statement of Operations (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 103,831	$ 107,871
Total operating expenses	79,289	75,245
Operating income (loss)	24,542	32,626
Total other non-operating income (expense)	6,051	3,151
Income Before Income Taxes	30,593	35,777
Income tax expense	10,868	14,010
Net income (loss)	19,725	21,767
Noncontrolling interests	(383)	171
Net income (loss) attributable to the Company	19,342	21,938
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	104,232	107,855
Total operating expenses	78,471	74,914
Operating income (loss)	25,761	32,941
Total other non-operating income (expense)	4,415	2,997
Income Before Income Taxes	30,176	35,938
Income tax expense	10,868	14,010
Net income (loss)	19,308	21,928
Noncontrolling interests	34	10
Net income (loss) attributable to the Company	19,342	21,938
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0
Total operating expenses	1,219	315
Operating income (loss)	(1,219)	(315)
Total other non-operating income (expense)	4,914	910
Income Before Income Taxes	3,695	595
Income tax expense	0
Net income (loss)	3,695	595
Noncontrolling interests	0
Net income (loss) attributable to the Company	3,695	595
Eliminations and Adjustments [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	(401)	16
Total operating expenses	(401)	16
Operating income (loss)	0
Total other non-operating income (expense)	(3,278)	(756)
Income Before Income Taxes	(3,278)	(756)
Income tax expense	0
Net income (loss)	(3,278)	(756)
Noncontrolling interests	(417)	161
Net income (loss) attributable to the Company	$ (3,695)	$ (595)