v2.4.0.8
Financial Instruments and Fair Value , Investments (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 726,001 $ 614,853
Unrealized Gains 1,565 1,925
Unrealized Losses (394) (167)
Total 727,172 616,611
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 205,428 141,470
Less Than 12 Months, Unrealized Losses (394) (162)
12 Months or Greater, Fair Value 500 5,010
12 Months or Greater, Unrealized Losses 0 (5)
Total, Fair Value 205,928 146,480
Total, Unrealized Losses (394) (167)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Due within one year 375,497 290,719
Due within one to three years 351,675 325,892
Total 727,172 616,611
U.S. government and agency securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 2,000  
Unrealized Gains 1  
Unrealized Losses 0  
Total 2,001  
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Total 2,001  
Corporate debt securities [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 603,185 529,738
Unrealized Gains 1,506 1,814
Unrealized Losses (374) (161)
Total 604,317 531,391
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 182,795 133,006
Less Than 12 Months, Unrealized Losses (374) (156)
12 Months or Greater, Fair Value 500 5,010
12 Months or Greater, Unrealized Losses 0 (5)
Total, Fair Value 183,295 138,016
Total, Unrealized Losses (374) (161)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Total 604,317 531,391
Commercial paper [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 69,356 39,229
Unrealized Gains 7 22
Unrealized Losses 0 (6)
Total 69,363 39,245
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 7,897 8,464
Less Than 12 Months, Unrealized Losses 0 (6)
12 Months or Greater, Fair Value 0 0
12 Months or Greater, Unrealized Losses 0 0
Total, Fair Value 7,897 8,464
Total, Unrealized Losses 0 (6)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Total 69,363 39,245
Municipal bonds [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 38,815 36,787
Unrealized Gains 48 83
Unrealized Losses (20) 0
Total 38,843 36,870
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]    
Less Than 12 Months, Fair Value 14,736  
Less Than 12 Months, Unrealized Losses (20)  
12 Months or Greater, Fair Value 0  
12 Months or Greater, Unrealized Losses 0  
Total, Fair Value 14,736  
Total, Unrealized Losses (20)  
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Total 38,843 36,870
Certificates of deposit and term deposits [Member]
    
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 12,645 9,099
Unrealized Gains 3 6
Unrealized Losses 0 0
Total 12,648 9,105
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]    
Total $ 12,648 $ 9,105