Fair Value Measurements - Financial assets measured at fair value on a recurring basis (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013
Cash And Cash Equivalents
Assets			$ 1,000
Marketable Securities
Assets			800
Cash, including short-term deposits
Assets	57,385	[1]	72,602
Cash, including short-term deposits | Level 1
Assets	57,385	[1]	72,602
Cash, including short-term deposits | Level 2
Assets	0	[1]	0
Cash, including short-term deposits | Level 3
Assets	0	[1]	0
Mutual funds
Assets	20,667	[2]	20,783
Mutual funds | Level 1
Assets	20,667	[2]	20,783
Mutual funds | Level 2
Assets	0	[2]	0
Mutual funds | Level 3
Assets	0	[2]	0
United States government securities
Assets	23,915	[2]	50,379
United States government securities | Level 1
Assets	23,915	[2]	50,379
United States government securities | Level 2
Assets	0	[2]	0
United States government securities | Level 3
Assets	0	[2]	0
Corporate securities
Assets	115,196	[2]	74,559
Corporate securities | Level 1
Assets	107,259	[2]	68,624
Corporate securities | Level 2
Assets	0	[2]	0
Corporate securities | Level 3
Assets	7,937	[2]	5,935
Commercial paper
Assets	4,499	[3]	1,799
Commercial paper | Cash And Cash Equivalents
Assets	2,900
Commercial paper | Marketable Securities
Assets	1,600
Commercial paper | Level 1
Assets	0	[3]	0
Commercial paper | Level 2
Assets	4,499	[3]	1,799
Commercial paper | Level 3
Assets	0	[3]	0
Corporate obligations
Assets	37,588	[2]	31,965
Corporate obligations | Level 1
Assets	0	[2]	0
Corporate obligations | Level 2
Assets	15,960	[2]	14,535
Corporate obligations | Level 3
Assets	21,628	[2]	17,430
Investments in certain funds
Assets	826	[4]	844
Investments in certain funds | Level 1
Assets	0	[4]	0
Investments in certain funds | Level 2
Assets	0	[4]	0
Investments in certain funds | Level 3
Assets	826	[4]	844
Financial Assets
Assets	260,076		252,931
Financial Assets | Level 1
Assets	209,226		212,388
Financial Assets | Level 2
Assets	20,459		16,334
Financial Assets | Level 3
Assets	$ 30,391		$ 24,209

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

[2] Reported within “Marketable securities”

[3] within "Cash and cash equivalents" and $1.6 million reported within "Marketable securities."

[4] Reported within "Other investments".