Consolidation of Sponsored Investment Products - Consolidated Statement of Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Current assets	$ 164,826		$ 92,595
Non-current assets	167,923
Total assets	332,749		286,379
Current liabilities	62,411		46,657
Other non-current liabilities	22,704
Total liabilities	85,115		68,007
Redeemable noncontrolling interest	3,163
Equity attributable to stockholders of the Company	244,474		183,155
Non-redeemable noncontrolling interest	(3)
Total liabilities and stockholders' equity	332,749		286,379
Before Consolidation [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	161,286
Non-current assets	167,923
Total assets	329,209
Current liabilities	62,034
Other non-current liabilities	22,704
Total liabilities	84,738
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	244,474
Non-redeemable noncontrolling interest	(3)
Total liabilities and stockholders' equity	329,209
Consolidated Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	43,924
Non-current assets
Total assets	43,924
Current liabilities	364
Other non-current liabilities
Total liabilities	364
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	43,560
Non-redeemable noncontrolling interest
Total liabilities and stockholders' equity	43,924
Eliminations [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	(40,384)	[1]
Non-current assets		[1]
Total assets	(40,384)	[1]
Current liabilities	13	[1]
Other non-current liabilities		[1]
Total liabilities	13	[1]
Redeemable noncontrolling interest	3,163	[1]
Equity attributable to stockholders of the Company	(43,560)	[1]
Non-redeemable noncontrolling interest		[1]
Total liabilities and stockholders' equity	$ (40,384)	[1]

[1] Adjustments include the elimination of intercompany transactions between the Company and its consolidated sponsored investment products, primarily the elimination of the investments and equity and recording of any noncontrolling interest.