Cash Equivalents and Investments - Gross Unrealized Losses and Fair Value of Company's Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value	$ 55,342	$ 56,581
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(754)	(1,024)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	3,728	4,141
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(80)	(79)
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	47,476	38,280
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(749)	(1,018)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	3,728	4,141
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(80)	(79)
Government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Fair Value	4,910	18,301
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(2)	(6)
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	2,956
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(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