Cash, Cash Equivalents, and Investments - Gross Unrealized Losses and Fair Values for Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	$ 119,810
Unrealized Losses, Less than 12 Months	(411)
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	45,301
Unrealized Losses, Less than 12 Months	(66)
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	43,706
Unrealized Losses, Less than 12 Months	(291)
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	13,371
Unrealized Losses, Less than 12 Months	(33)
Treasury bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	12,498
Unrealized Losses, Less than 12 Months	(1)
Covered bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	2,937
Unrealized Losses, Less than 12 Months	(17)
Sovereign bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 Months	1,997
Unrealized Losses, Less than 12 Months	$ (3)