Cash, Cash Equivalents and Investments - Gross Unrealized Losses and Fair Value For Available-For-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	$ 110,949
Unrealized Loss Position Less than 12 Month	(106)
Treasury Bills [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	38,529
Unrealized Loss Position Less than 12 Month	(7)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	30,573
Unrealized Loss Position Less than 12 Month	(41)
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	17,333
Unrealized Loss Position Less than 12 Month	(19)
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	12,558
Unrealized Loss Position Less than 12 Month	(20)
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	4,828
Unrealized Loss Position Less than 12 Month	(2)
Covered Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	4,664
Unrealized Loss Position Less than 12 Month	(15)
Sovereign Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Less than 12 months	2,464
Unrealized Loss Position Less than 12 Month	$ (2)