Consolidation of Sponsored Investment Products - Consolidated Statement of Balance Sheet (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Current assets	$ 154,211	$ 164,826
Non-current assets	160,521	167,923
Total assets	314,732	332,749
Current liabilities	44,919	62,411
Non-current liabilities	22,544	22,704
Total liabilities	67,463	85,115
Redeemable noncontrolling interest	2,142	3,163
Equity attributable to stockholders of the Company	245,148	244,474
Non-redeemable noncontrolling interest	(21)	(3)
Total liabilities and equity	314,732	332,749
Balance Before Consolidation of Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	151,452	161,286
Non-current assets	160,521	167,923
Total assets	311,973	329,209
Current liabilities	44,302	62,034
Non-current liabilities	22,544	22,704
Total liabilities	66,846	84,738
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	245,148	244,474
Non-redeemable noncontrolling interest	(21)	(3)
Total liabilities and equity	311,973	329,209
Consolidated Investment Products [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	37,872	43,924
Non-current assets
Total assets	37,872	43,924
Current liabilities	622	364
Non-current liabilities
Total liabilities	622	364
Redeemable noncontrolling interest
Equity attributable to stockholders of the Company	37,250	43,560
Non-redeemable noncontrolling interest
Total liabilities and equity	37,872	43,924
Eliminations and Adjustments [Member]
Condensed Financial Statements, Captions [Line Items]
Current assets	(35,113)	(40,384)
Non-current assets
Total assets	(35,113)	(40,384)
Current liabilities	(5)	13
Non-current liabilities
Total liabilities	(5)	13
Redeemable noncontrolling interest	2,142	3,163
Equity attributable to stockholders of the Company	(37,250)	(43,560)
Non-redeemable noncontrolling interest
Total liabilities and equity	$ (35,113)	$ (40,384)