Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial instrument obligations
Liabilities	$ (21,308)	$ (21,311)
Cash, including short-term deposits
Assets	64,076	51,910
Restricted cash
Assets	21,308
Mutual funds
Assets	21,471	20,970
Corporate securities
Assets	72,078	87,850
Corporate obligations
Assets	30,836	29,637
Investments in equity-method investees
Assets	33,240
Investments in certain funds
Assets	483	525
Financial Assets
Assets	243,492	190,892
Level 1 | Financial instrument obligations
Liabilities	(21,308)	(21,311)
Level 1 | Cash, including short-term deposits
Assets	64,076	51,910
Level 1 | Restricted cash
Assets	21,308
Level 1 | Mutual funds
Assets	21,471	20,970
Level 1 | Corporate securities
Assets	59,890	72,798
Level 1 | Corporate obligations
Assets	0	0
Level 1 | Investments in equity-method investees
Assets	33,240
Level 1 | Investments in certain funds
Assets	0	0
Level 1 | Financial Assets
Assets	199,985	145,678
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	12,134	10,793
Level 2 | Investments in equity-method investees
Assets	0
Level 2 | Investments in certain funds
Assets	0	0
Level 2 | Financial Assets
Assets	12,134	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	12,188	15,052
Level 3 | Corporate obligations
Assets	18,702	18,844
Level 3 | Investments in equity-method investees
Assets	0
Level 3 | Investments in certain funds
Assets	483	525
Level 3 | Financial Assets
Assets	$ 31,373	$ 34,421