Gross Unrealized Losses and Fair Values of Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	$ 10,568
Less than 12 Months, Unrealized Loss	(5)
Corporate obligations
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	3,810
Less than 12 Months, Unrealized Loss	(1)
U.S. Government notes
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months Fair Value	6,758
Less than 12 Months, Unrealized Loss	$ (4)