Available-For-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 139,006		$ 285,205
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,923	[1]	2,007	[1]
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	8,131	[2],[3]	9,869	[2],[3]
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,742	[4]	4,168	[4]
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	123,210
U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities			269,161	[5]
Level 2
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	132,976		8,672
Level 2 | Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,923	[1]	2,007	[1]
Level 2 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,101	[3]	2,497	[3]
Level 2 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,742	[4]	4,168	[4]
Level 2 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	123,210
Level 3
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	6,030		7,372
Level 3 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	6,030	[3]	7,372	[3]
Level 1
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities			269,161
Level 1 | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities			$ 269,161	[5]

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

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

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

[4] Corporate notes and bonds with maturities of three years or less

[5] Investments in U.S. Treasury securities, which were sold during 2011