Investments - Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Marketable Securities [Abstract]
Cost	$ 44,482	$ 50,629
Unrealized Loss	(1,236)	(1,353)
Unrealized Gain	1,002	975
Fair Value	44,248	50,251
Sponsored Funds [Member]
Marketable Securities [Abstract]
Cost	31,942	39,079
Unrealized Loss	(997)	(1,190)
Unrealized Gain	688	423
Fair Value	31,633	38,312
Equity Securities [Member]
Marketable Securities [Abstract]
Cost	9,301	8,421
Unrealized Loss	(12)
Unrealized Gain	176	319
Fair Value	9,465	8,740
Sponsored Closed-End Funds [Member]
Marketable Securities [Abstract]
Cost	3,239	3,129
Unrealized Loss	(227)	(163)
Unrealized Gain	138	233
Fair Value	$ 3,150	$ 3,199