Available-For-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 143,409		$ 289,544
Gross Unrealized Gains	22		41
Gross Unrealized Losses	(4,425)		(4,380)
Estimated Fair Value	139,006		285,205
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,489	[1]	14,248	[1]
Gross Unrealized Losses	(4,358)	[1]	(4,379)	[1]
Estimated Fair Value	8,131	[1],[2]	9,869	[1],[2]
Corporate and foreign government bonds and notes
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,750		4,167
Gross Unrealized Gains			1
Gross Unrealized Losses	(8)
Estimated Fair Value	5,742		4,168
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,975
Gross Unrealized Losses	(52)
Estimated Fair Value	1,923	[3]	2,007	[3]
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	123,195
Gross Unrealized Gains	22
Gross Unrealized Losses	(7)
Estimated Fair Value	123,210
U.S. Treasury securities and obligations of U.S. Government agencies
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			269,154
Gross Unrealized Gains			8
Gross Unrealized Losses			(1)
Estimated Fair Value			269,161
Money market instruments and short-term investments
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost			1,975
Gross Unrealized Gains			32
Estimated Fair Value			$ 2,007

[1] Included in our asset-backed securities and collateralized mortgage obligations is approximately $7.4 million of commercial paper secured by mortgaged-backed securities.

[2] Asset-backed and mortgage-backed securities with maturities of up to 26 years

[3] Various U.S. equities and other investments managed under mutual funds