Schedule of Unrealized Loss on Available for Sale for sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Market Value	$ 17,748	$ 7,126
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	14	145
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Market Value	478
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	21
Available-for-sale investments with unrealized losses, Fair Market Value, Total	18,226	7,126
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	35	145
Mortgage-backed securities
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Market Value	546	468
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	1	18
Available-for-sale investments with unrealized losses, Fair Market Value, Total	546	468
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	1	18
Corporate bonds and direct obligations of government agencies
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Market Value	5,911	6,067
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	11	126
Available-for-sale investments with unrealized losses, 12 months or longer, Fair Market Value	478
Available-for-sale investments with unrealized losses, 12 months or longer, Unrealized Loss	21
Available-for-sale investments with unrealized losses, Fair Market Value, Total	6,389	6,067
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	32	126
U.S. Treasury Obligations
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale investments with unrealized losses, Less than 12 months, Fair Market Value	11,291	591
Available-for-sale investments with unrealized losses, Less than 12 months, Unrealized Loss	2	1
Available-for-sale investments with unrealized losses, Fair Market Value, Total	11,291	591
Available-for-sale investments with unrealized losses, Unrealized Loss, Total	$ 2	$ 1