Investments - Schedule of Marketable Securities (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Marketable Securities [Abstract]
Cost	$ 51,333	$ 25,937
Unrealized Loss	(548)	(849)
Unrealized Gain	5,618	3,880
Fair Value	56,403	28,968
Sponsored Funds [Member]
Marketable Securities [Abstract]
Cost	40,403	16,079
Unrealized Loss	(453)	(704)
Unrealized Gain	4,031	2,529
Fair Value	43,981	17,904
Cost	3,019	2,815
Unrealized Loss	(95)	(145)
Unrealized Gain	265	15
Fair Value	3,189	2,685
Equity Securities [Member]
Marketable Securities [Abstract]
Cost	7,911	7,043
Unrealized Loss	0	0
Unrealized Gain	1,322	1,336
Fair Value	$ 9,233	$ 8,379