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Investments (Details) (USD $)
In Thousands, unless otherwise specified
9 Months Ended 12 Months Ended
Sep. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost $ 23,312 $ 32,515
Gross Unrealized Gains 605 430
Gross Unrealized Losses      
Fair Value 23,917 32,945
Auction Rate Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 1,175 1,175
Gross Unrealized Gains 601 409
Gross Unrealized Losses      
Fair Value 1,776 1,584
Corporate Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Amortized Cost 22,137 31,340
Gross Unrealized Gains 4 21
Gross Unrealized Losses      
Fair Value $ 22,141 $ 31,361