Consolidated Sponsored Investment Products - Assets Related to Consolidated Sponsored Investment Products, Unobservable Input Reconciliation (Detail) - Consolidated Sponsored Investment Products [Member] - Debt Securities [Member] - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 1,065	$ 0
Purchases	135	450
Paydowns	(14)	(2)
Sales	(13)	0
Transferred to Level 2	(126)	0
Change in unrealized gain/(loss), net	(121)	(1)
Balance at end of period	$ 926	$ 447