Investments - Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Available-for-sale:
Cost	$ 43,956	$ 50,629
Unrealized Loss	(2,885)	(1,353)
Unrealized Gain	425	975
Fair Value	41,496	50,251
Sponsored funds [Member]
Trading:
Cost	31,167	39,079
Unrealized Loss	(2,134)	(1,190)
Unrealized Gain	298	423
Fair Value	29,331	38,312
Equity securities [Member]
Trading:
Cost	9,434	8,421
Unrealized Loss	(386)	0
Unrealized Gain	120	319
Fair Value	9,168	8,740
Sponsored closed-end funds [Member]
Available-for-sale:
Cost	3,355	3,129
Unrealized Loss	(365)	(163)
Unrealized Gain	7	233
Fair Value	$ 2,997	$ 3,199