Consolidation - Condensed Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Condensed Income Statements, Captions [Line Items]
Total operating revenues	$ 92,375	$ 117,841	$ 295,862	$ 338,461
Total operating expenses	69,253	78,914	231,990	244,406
Operating Income	23,122	38,927	63,872	94,055
Total other non-operating expense	(17,156)	(3,737)	(10,478)	8,810
Income Before Income Taxes	5,966	35,190	53,394	102,865
Income tax expense (benefit)	9,669	(1,805)	28,360	24,311
Net (Loss) Income	(3,703)	36,995	25,034	78,554
Noncontrolling interests	3,054	345	3,436	267
Net (Loss) Income Attributable to Common Stockholders	(649)	37,340	28,470	78,821
Reportable Legal Entities [Member] | Balance Before Consolidation of Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	92,804	117,808	297,089	338,534
Total operating expenses	68,134	77,668	229,096	242,032
Operating Income	24,670	40,140	67,993	96,502
Total other non-operating expense	(15,557)	(4,649)	(11,269)	6,545
Income Before Income Taxes	9,113	35,491	56,724	103,047
Income tax expense (benefit)	9,669	(1,805)	28,360	24,311
Net (Loss) Income	(556)	37,296	28,364	78,736
Noncontrolling interests	(93)	44	106	85
Net (Loss) Income Attributable to Common Stockholders	(649)	37,340	28,470	78,821
Reportable Legal Entities [Member] | Consolidated Sponsored Investment Products [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0	0	0	0
Total operating expenses	1,548	1,213	4,121	2,447
Operating Income	(1,548)	(1,213)	(4,121)	(2,447)
Total other non-operating expense	(14,723)	(3,109)	(9,951)	5,883
Income Before Income Taxes	(16,271)	(4,322)	(14,072)	3,436
Income tax expense (benefit)	0	0	0	0
Net (Loss) Income	$ (16,271)	(4,322)	(14,072)	3,436
Noncontrolling interests		0	0	0
Net (Loss) Income Attributable to Common Stockholders	$ (16,271)	(4,322)	(14,072)	3,436
Reportable Legal Entities [Member] | Consolidated Investment Product [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	0	0	0	0
Total operating expenses	0	0	0	0
Operating Income	0	0	0	0
Total other non-operating expense	(679)	0	(680)	0
Income Before Income Taxes	(679)	0	(680)	0
Income tax expense (benefit)	0	0	0	0
Net (Loss) Income	(679)	0	(680)	0
Noncontrolling interests	0	0	0	0
Net (Loss) Income Attributable to Common Stockholders	(679)	0	(680)	0
Eliminations and Adjustments [Member]
Condensed Income Statements, Captions [Line Items]
Total operating revenues	(429)	33	(1,227)	(73)
Total operating expenses	(429)	33	(1,227)	(73)
Operating Income	0	0	0	0
Total other non-operating expense	13,803	4,021	11,422	(3,618)
Income Before Income Taxes	13,803	4,021	11,422	(3,618)
Income tax expense (benefit)	0	0	0	0
Net (Loss) Income	13,803	4,021	11,422	(3,618)
Noncontrolling interests	3,147	301	3,330	182
Net (Loss) Income Attributable to Common Stockholders	$ 16,950	$ 4,322	$ 14,752	$ (3,436)