Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Financial instrument obligations
Liabilities	$ 20,171	$ 21,311
Cash, including short-term deposits
Assets	69,746	51,910
Restricted cash
Assets	20,171
Mutual funds
Assets	13,500	20,970
Corporate securities
Assets	83,291	87,850
Corporate obligations
Assets	29,844	29,637
Investments in equity-method investees
Assets	33,177	24,355
Investments in certain funds
Assets	489	525
Financial Assets
Assets	250,218	215,247
Level 1 | Financial instrument obligations
Liabilities	20,171	21,311
Level 1 | Cash, including short-term deposits
Assets	69,746	51,910
Level 1 | Restricted cash
Assets	20,171
Level 1 | Mutual funds
Assets	13,500	20,970
Level 1 | Corporate securities
Assets	72,397	72,798
Level 1 | Corporate obligations
Assets	0	0
Level 1 | Investments in equity-method investees
Assets	33,177	24,355
Level 1 | Investments in certain funds
Assets	0	0
Level 1 | Financial Assets
Assets	208,991	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	8,709	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	8,709	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	10,894	15,052
Level 3 | Corporate obligations
Assets	21,135	18,844
Level 3 | Investments in equity-method investees
Assets	0	0
Level 3 | Investments in certain funds
Assets	489	525
Level 3 | Financial Assets
Assets	$ 32,518	$ 34,421