Available-for-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands	Jun. 30, 2011		Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 238,620		$ 285,205
Level 1
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	78,494		269,161
Level 1 | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	78,494	[1]	269,161
Level 2
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	153,054		8,672
Level 2 | Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,081	[2]	2,007
Level 2 | Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	142,862
Level 2 | U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,748	[1]
Level 2 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,363	[3]	2,497
Level 2 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities			4,168
Level 3
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	7,072		7,372
Level 3 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	7,072	[3]	7,372
Mutual Funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,081	[2]	2,007
Commercial Paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	142,862
U.S. Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	84,242	[1]	269,161
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	9,435	[3]	9,869
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities			$ 4,168

[1] Investments in U.S. Treasury securities with maturities of two years or less.

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

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