Quarterly report pursuant to Section 13 or 15(d)

Fair Value (Details)

v2.4.0.6
Fair Value (Details) (Recurring basis, USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Level 1
   
Fair Value    
Investments at fair value $ 9,053 $ 23,936
Level 1 | Money market funds
   
Fair Value    
Investments at fair value 9,053 23,936
Level 2
   
Fair Value    
Investments at fair value 263,240 274,054
Level 2 | Government-sponsored enterprise securities
   
Fair Value    
Investments at fair value 75,233 77,047
Level 2 | Corporate bonds and commercial paper
   
Fair Value    
Investments at fair value 188,007 197,007
Total
   
Fair Value    
Investments at fair value 272,293 297,990
Total | Money market funds
   
Fair Value    
Investments at fair value 9,053 23,936
Total | Government-sponsored enterprise securities
   
Fair Value    
Investments at fair value 75,233 77,047
Total | Corporate bonds and commercial paper
   
Fair Value    
Investments at fair value $ 188,007 $ 197,007