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Fair Value Measurements (Details) (USD $)
In Thousands, unless otherwise specified
3 Months Ended 3 Months Ended
Mar. 31, 2013
Dec. 31, 2012
Mar. 31, 2013
Auction Rate Securities [Member]
Mar. 31, 2012
Auction Rate Securities [Member]
Mar. 31, 2013
Maximum [Member]
Mar. 31, 2013
Minimum [Member]
Mar. 31, 2013
Weighted average [Member]
Mar. 31, 2013
U.S. Government Subsidized Securities [Member]
Significant Unobservable Inputs (Level 3) [Member]
Mar. 31, 2013
Investment Company Perpetual Preferred Stock [Member]
Significant Unobservable Inputs (Level 3) [Member]
Mar. 31, 2013
Recurring [Member]
Dec. 31, 2012
Recurring [Member]
Mar. 31, 2013
Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Dec. 31, 2012
Recurring [Member]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Mar. 31, 2013
Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Dec. 31, 2012
Recurring [Member]
Significant Other Observable Inputs (Level 2) [Member]
Mar. 31, 2013
Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Dec. 31, 2012
Recurring [Member]
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]                                  
Money Market Funds                   $ 49,336 $ 56,224 $ 49,336 $ 56,224 $ 0 $ 0 $ 0 $ 0
Auction Rate Securities 3,148 3,240           2,208 940 3,148 3,240 0 0 0 0 3,148 3,240
Investment, total                   52,484 59,464 49,336 56,224 0 0 3,148 3,240
Maturity period of US government subsidized securities (in years) 10 years                                
Redemption period of auction rate securities (in years)         15 years 4 years 5 years 10 months 24 days                    
Discount rate for valuing auction rate securities (in hundredths)         2.102% 0.125% 0.71%                    
Duration of securities subject to temporary impairment, minimum (in months) 12 months                                
Amount of temporary impairment 252 260                              
Summary of activities in financial instruments with significant Level 3 inputs [Roll Forward]                                  
Balance at beginning of period     3,240 3,332                          
Transfers into Level 3     0 0                          
Transfers out of Level 3     0 0                          
Total gains (losses)                                  
Included in net loss     0 0                          
Included in other comprehensive loss     8 8                          
Settlements at par     (100) (100)                          
Balance at end of period     3,148 3,240                          
Changes in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period     $ 0 $ 0