Available-For-Sale Securities (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 48,306		$ 143,409
Gross Unrealized Gains	62		22
Gross Unrealized Losses	(2,376)		(4,425)
Estimated Fair Value	45,992		139,006
Mutual funds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,975	[1]	1,975	[1]
Gross Unrealized Gains	48	[1]
Gross Unrealized Losses			(52)	[1]
Estimated Fair Value	2,023	[1]	1,923	[1]
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29,728	[2]	123,195	[2]
Gross Unrealized Gains	9	[2]	22	[2]
Gross Unrealized Losses			(7)	[2]
Estimated Fair Value	29,737	[2]	123,210	[2]
Asset-backed securities and collateralized mortgage obligations
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,853	[3],[4]	12,489	[3],[5]
Gross Unrealized Losses	(2,376)	[3],[4]	(4,358)	[3],[5]
Estimated Fair Value	8,477	[3],[4]	8,131	[3],[5]
Corporate notes and bonds
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,750	[6]	5,750	[6]
Gross Unrealized Gains	5	[6]
Gross Unrealized Losses			(8)	[6]
Estimated Fair Value	$ 5,755	[6]	$ 5,742	[6]

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

[2] Commercial paper with maturities less than one year.

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

[4] Included in our asset-backed securities and collateralized mortgage obligations is approximately $6.3 million of commercial paper secured by mortgaged-backed securities.

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

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