Consolidated Sponsored Investment Products - Condensed Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 99,656	$ 112,749	$ 203,487	$ 220,620
Total operating expenses	83,448	90,247	162,737	165,492
Operating income (loss)	16,208	22,502	40,750	55,128
Total other non-operating income (expense)	627	9,396	6,678	12,547
Income Before Income Taxes	16,835	31,898	47,428	67,675
Income tax expense	7,823	12,106	18,691	26,116
Net income (loss)	9,012	19,792	28,737	41,559
Noncontrolling interests	765	(249)	382	(78)
Net income (loss) attributable to the Company	9,777	19,543	29,119	41,481
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	100,052	112,871	204,284	220,726
Total operating expenses	82,491	89,450	160,962	164,364
Operating income (loss)	17,561	23,421	43,322	56,362
Total other non-operating income (expense)	(127)	8,198	4,288	11,195
Income Before Income Taxes	17,434	31,619	47,610	67,557
Income tax expense	7,823	12,106	18,691	26,116
Net income (loss)	9,611	19,513	28,919	41,441
Noncontrolling interests	166	30	200	40
Net income (loss) attributable to the Company	9,777	19,543	29,119	41,481
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating expenses	1,353	919	2,572	1,234
Operating income (loss)	(1,353)	(919)	(2,572)	(1,234)
Total other non-operating income (expense)	(144)	8,082	4,770	8,992
Income Before Income Taxes	(1,497)	7,163	2,198	7,758
Net income (loss)	(1,497)	7,163	2,198	7,758
Net income (loss) attributable to the Company	(1,497)	7,163	2,198	7,758
Eliminations and Adjustments [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	(396)	(122)	(797)	(106)
Total operating expenses	(396)	(122)	(797)	(106)
Total other non-operating income (expense)	898	(6,884)	(2,380)	(7,640)
Income Before Income Taxes	898	(6,884)	(2,380)	(7,640)
Net income (loss)	898	(6,884)	(2,380)	(7,640)
Noncontrolling interests	599	(279)	182	(118)
Net income (loss) attributable to the Company	$ 1,497	$ (7,163)	$ (2,198)	$ (7,758)