Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014		Dec. 31, 2013
Cash And Cash Equivalents
Assets			$ 1,000
Marketable Securities
Assets			800
Financial instrument obligations
Liabilities	20,010
Cash, including short-term deposits
Assets	69,432	[1]	72,602	[2]
Restricted cash
Assets	20,010
Mutual funds
Assets	21,734	[3]	20,783	[4]
United States government securities
Assets			50,379	[4]
Corporate securities
Assets	101,640	[3]	74,559	[4]
Commercial paper
Assets			1,799	[5]
Corporate obligations
Assets	33,889	[3]	31,965	[4]
Investments in equity-method investees
Assets	31,330
Investments in certain funds
Assets	540	[6]	844	[7]
Financial Assets
Assets	278,575		252,931
Level 1 | Financial instrument obligations
Liabilities	20,010
Level 1 | Cash, including short-term deposits
Assets	69,432	[1]	72,602	[2]
Level 1 | Restricted cash
Assets	20,010
Level 1 | Mutual funds
Assets	21,734	[3]	20,783	[4]
Level 1 | United States government securities
Assets			50,379	[4]
Level 1 | Corporate securities
Assets	89,176	[3]	68,624	[4]
Level 1 | Commercial paper
Assets			0	[5]
Level 1 | Corporate obligations
Assets	0	[3]	0	[4]
Level 1 | Investments in equity-method investees
Assets	31,330
Level 1 | Investments in certain funds
Assets	0	[6]	0	[7]
Level 1 | Financial Assets
Assets	231,682		212,388
Level 2 | Financial instrument obligations
Liabilities	0
Level 2 | Cash, including short-term deposits
Assets	0	[1]	0	[2]
Level 2 | Restricted cash
Assets	0
Level 2 | Mutual funds
Assets	0	[3]	0	[4]
Level 2 | United States government securities
Assets			0	[4]
Level 2 | Corporate securities
Assets	0	[3]	0	[4]
Level 2 | Commercial paper
Assets			1,799	[5]
Level 2 | Corporate obligations
Assets	14,547	[3]	14,535	[4]
Level 2 | Investments in equity-method investees
Assets	0
Level 2 | Investments in certain funds
Assets	0	[6]	0	[7]
Level 2 | Financial Assets
Assets	14,547		16,334
Level 3 | Financial instrument obligations
Liabilities	0
Level 3 | Cash, including short-term deposits
Assets	0	[1]	0	[2]
Level 3 | Restricted cash
Assets	0
Level 3 | Mutual funds
Assets	0	[3]	0	[4]
Level 3 | United States government securities
Assets			0	[4]
Level 3 | Corporate securities
Assets	12,464	[3]	5,935	[4]
Level 3 | Commercial paper
Assets			0	[5]
Level 3 | Corporate obligations
Assets	19,342	[3]	17,430	[4]
Level 3 | Investments in equity-method investees
Assets	0
Level 3 | Investments in certain funds
Assets	540	[6]	844	[7]
Level 3 | Financial Assets
Assets	$ 32,346		$ 24,209

[1] Reported within "Cash and cash equivalents"

[2] Reported within "Cash and cash equivalents."

[3] Reported within “Marketable securities”

[4] Reported within “Marketable securities.”

[5] reported within "Cash and cash equivalents" and $0.8 million reported within "Marketable securities."

[6] Reported within "Other investments"

[7] Reported within "Other investments."