Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Assets		$ 24,355
Financial instrument obligations
Liabilities	$ 21,385	21,311
Cash, including short-term deposits
Assets	63,907	51,910
Restricted cash
Assets	21,385
Mutual funds
Assets	16,361	20,970
Corporate securities
Assets	73,437	87,850
Corporate obligations
Assets	34,298	29,637
Investments in equity-method investees
Assets	38,834	24,355
Investments in certain funds
Assets	467	525
Financial Assets
Assets	248,689	215,247
Level 1 | Financial instrument obligations
Liabilities	21,385	21,311
Level 1 | Cash, including short-term deposits
Assets	63,907	51,910
Level 1 | Restricted cash
Assets	21,385
Level 1 | Mutual funds
Assets	16,361	20,970
Level 1 | Corporate securities
Assets	62,044	72,798
Level 1 | Corporate obligations
Assets	0	0
Level 1 | Investments in equity-method investees
Assets	38,834	24,355
Level 1 | Investments in certain funds
Assets	0	0
Level 1 | Financial Assets
Assets	202,531	170,033
Level 2 | Financial instrument obligations
Liabilities	0	0
Level 2 | Cash, including short-term deposits
Assets	0	0
Level 2 | Restricted cash
Assets	0
Level 2 | Mutual funds
Assets	0	0
Level 2 | Corporate securities
Assets	0	0
Level 2 | Corporate obligations
Assets	10,675	10,793
Level 2 | Investments in equity-method investees
Assets	0	0
Level 2 | Investments in certain funds
Assets	0	0
Level 2 | Financial Assets
Assets	10,675	10,793
Level 3 | Financial instrument obligations
Liabilities	0	0
Level 3 | Cash, including short-term deposits
Assets	0	0
Level 3 | Restricted cash
Assets	0
Level 3 | Mutual funds
Assets	0	0
Level 3 | Corporate securities
Assets	11,393	15,052
Level 3 | Corporate obligations
Assets	23,623	18,844
Level 3 | Investments in equity-method investees
Assets	0	0
Level 3 | Investments in certain funds
Assets	467	525
Level 3 | Financial Assets
Assets	$ 35,483	$ 34,421