Investments - Schedule of Marketable Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale:
Cost	$ 72,882	$ 75,862
Unrealized Loss	(1,401)	(2,207)
Unrealized Gain	4,221	1,252
Fair Value	75,702	74,907
Sponsored funds
Trading:
Cost	56,511	61,784
Unrealized Loss	(1,141)	(1,942)
Unrealized Gain	1,204	177
Fair Value	56,574	60,019
Equity securities
Trading:
Cost	12,677	10,578
Unrealized Loss	0	0
Unrealized Gain	2,555	895
Fair Value	15,232	11,473
Sponsored closed-end funds
Available-for-sale:
Cost	3,694	3,500
Unrealized Loss	(260)	(265)
Unrealized Gain	462	180
Fair Value	$ 3,896	$ 3,415

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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