Available-for-Sale Securities Measured at Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 58,834		$ 139,006
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,998	[1]	1,923
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	42,480		123,210
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	8,595	[2]	8,131
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,761	[3]	5,742
Level 2
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	52,377		132,976
Level 2 | Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	1,998	[1]	1,923
Level 2 | Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	42,480		123,210
Level 2 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	2,138	[2]	2,101
Level 2 | Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	5,761	[3]	5,742
Level 3
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	6,457		6,030
Level 3 | Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities	$ 6,457	[2]	$ 6,030

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

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

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