Cash Equivalents and Investments - Gross Unrealized Losses and Fair Values of Company's Short-Term Investments (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 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	$ 128,704	$ 56,581
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(2,760)	(1,024)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	6,598	4,141
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(200)	(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	67,133	38,280
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(2,138)	(1,018)
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Fair Value	6,598	4,141
Available-for-sale Securities, Continuous unrealized loss position, Greater than 12 Months, Unrealized Losses	(200)	(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	51,960	18,301
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(544)	(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	9,611
Available-for-sale Securities, Continuous unrealized loss position, Less than 12 Months, Unrealized Losses	(78)
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