Consolidated Sponsored Investment Products - Balances of Consolidated Sponsored Investment Products (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014	Dec. 31, 2013
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Total cash and cash equivalents	$ 128,847	$ 203,304	$ 173,764	$ 271,545
Total investments	55,225	63,448
Total liabilities	(237,538)	(112,350)
Redeemable noncontrolling interests	(49,895)	(23,071)
Consolidated Sponsored Investment Products [Member]
Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items]
Total cash and cash equivalents	16,732	8,687
Total investments	311,429	236,652
All other assets	10,494	6,960
Total liabilities	(29,849)	(12,556)
Redeemable noncontrolling interests	(49,895)	(23,071)
The Company’s net interests in investment products	$ 258,911	$ 216,672
The Company's net interest as a percentage of total investments of investment products	83.10%	91.60%