Cash Equivalents and Investments - Gross Unrealized Losses and Fair Value of Company's Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value	$ 56,581	$ 16,892
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(1,024)	(316)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	4,141	1,806
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(79)	(92)
Asset-backed and mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value	38,280	10,645
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(1,018)	(286)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	4,141	1,301
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(79)	(92)
Government and agencies securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value	18,301	3,872
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(6)	(3)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value		2,375
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses		(27)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value		505
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses