Investments in Unrealized Loss Position (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 960,464	$ 894,268
Less than 12 Months, Unrealized Loss	(1,315)	(700)
12 Months or Greater, Fair Value	3,833
12 Months or Greater, Unrealized Loss	(2)
Total, Fair Value	964,297	894,268
Total, Unrealized Loss	(1,317)	(700)
Government and agency securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	263,514	165,025
Less than 12 Months, Unrealized Loss	(101)	(45)
Total, Fair Value	263,514	165,025
Total, Unrealized Loss	(101)	(45)
Corporate Debt Securities, Commercial Paper, And Bank Certificates Of Deposit
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	696,950	729,046
Less than 12 Months, Unrealized Loss	(1,214)	(622)
12 Months or Greater, Fair Value	3,833
12 Months or Greater, Unrealized Loss	(2)
Total, Fair Value	700,783	729,046
Total, Unrealized Loss	(1,216)	(622)
Corporate Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		197
Less than 12 Months, Unrealized Loss		(33)
Total, Fair Value		197
Total, Unrealized Loss		$ (33)