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Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2012
Dec. 31, 2011
Dec. 31, 2010
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Auction rate securities $ 3,240 $ 3,332  
Duration of securities subject to temporary impairment, minimum (in months) 12 months    
Decrease in temporary impairment of auction rate securities 8    
Amount of temporary impairment 260 268  
Summarize the amortized cost basis, the aggregate fair value and gross unrealized holding [Abstract]      
Gross Unrealized Holding, Losses (260) (268)  
Continuous unrealized loss position, Fair Value [Abstract]      
Total, Fair Value 3,240 3,332  
Continuous unrealized loss position, Unrealized Losses [Abstract]      
Total, Unrealized Losses (260) (268)  
Weighted average duration of unrealized losses 58 months 46 months  
Total realized/unrealized gains (losses)      
Total amount of unrealized gains (losses) for the period included in other comprehensive loss attributable to the change in fair market value of related assets still held at the reporting date 8 24 15
U.S. Government Subsidized Securities [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Maturity period of US government subsidized securities (in years) 10 years    
U.S. Government Subsidized Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Auction rate securities 2,300    
Investment Company Perpetual Preferred Stock [Member] | Significant Unobservable Inputs (Level 3) [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Auction rate securities 940    
Recurring [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Money market funds 56,224 64,068  
Auction rate securities 3,240 0  
Investment, total 59,464 64,068  
Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Money market funds 56,224 64,068  
Auction rate securities 0 3,332  
Investment, total 56,224 67,400  
Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Money market funds 0 0  
Auction rate securities 0 0  
Investment, total 0 0  
Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Money market funds 0 0  
Auction rate securities 3,240 3,332  
Investment, total 3,240 3,332  
Minimum [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Redemption period of auction rate securities (in years) 4 years    
Discount rate for valuing auction rate securities (in hundredths) 0.125%    
Continuous unrealized loss position, Unrealized Losses [Abstract]      
Severity of the unrealized losses below amortized cost (in hundredths) 6.00% 6.00%  
Maximum [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Redemption period of auction rate securities (in years) 15 years    
Discount rate for valuing auction rate securities (in hundredths) 2.102%    
Continuous unrealized loss position, Unrealized Losses [Abstract]      
Severity of the unrealized losses below amortized cost (in hundredths) 8.00% 8.00%  
Weighted average [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Redemption period of auction rate securities (in years) 5 years 10 months 24 days    
Discount rate for valuing auction rate securities (in hundredths) 0.71%    
Auction Rate Securities [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Amount of temporary impairment 260 268  
Summarize the amortized cost basis, the aggregate fair value and gross unrealized holding [Abstract]      
Amortized Cost Basis 3,500 3,600  
Fair Value 3,240 3,332  
Gross Unrealized Holding, Gains 0 0  
Gross Unrealized Holding, Losses (260) (268)  
Gross Unrealized Holding Gains (Losses), Net (260) (268)  
Continuous unrealized loss position, Fair Value [Abstract]      
Less than 12 Months, Fair Value 0 0  
12 Months or Greater, Fair Value 3,240 3,332  
Continuous unrealized loss position, Unrealized Losses [Abstract]      
Less than 12 Months, Unrealized Losses 0 0  
12 Months or Greater, Unrealized Losses (260) (268)  
Summary of activities in financial instruments with significant Level 3 inputs [Roll Forward]      
Balance at beginning of period 3,332 3,608  
Transfers into Level 3 0 0  
Total realized/unrealized gains (losses)      
Included in net income (loss) 0 0  
Included in comprehensive income (loss) 8 24  
Settlements (100) (300)  
Balance at end of period 3,240 3,332  
Total amount of unrealized gains (losses) for the period included in other comprehensive loss attributable to the change in fair market value of related assets still held at the reporting date 0 0  
Auction Rate Securities [Member] | Maturities Greater Than Ten Years [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Amount of temporary impairment 200 208  
Summarize the amortized cost basis, the aggregate fair value and gross unrealized holding [Abstract]      
Amortized Cost Basis 2,500 2,600  
Fair Value 2,300 2,392  
Gross Unrealized Holding, Gains 0 0  
Gross Unrealized Holding, Losses (200) (208)  
Gross Unrealized Holding Gains (Losses), Net (200) (208)  
Auction Rate Securities [Member] | Investments Without Stated Maturity Dates [Member]
     
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]      
Amount of temporary impairment 60 60  
Summarize the amortized cost basis, the aggregate fair value and gross unrealized holding [Abstract]      
Amortized Cost Basis 1,000 1,000  
Fair Value 940 940  
Gross Unrealized Holding, Gains 0 0  
Gross Unrealized Holding, Losses (60) (60)  
Gross Unrealized Holding Gains (Losses), Net $ (60) $ (60)