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Fair Value Disclosures (Narrative) (Detail) (USD $)
Jun. 30, 2012
Jun. 29, 2012
Jun. 30, 2012
Fair Value, Measurements, Nonrecurring [Member]
Jun. 30, 2012
US Treasury Notes Securities [Member]
Dec. 31, 2011
US Treasury Notes Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]          
Available-for-sale securities, debt maturities, period       July, September and December of 2012 January and May of 2012
Available-for-sale securities, amortized cost       $ 199,900,000 $ 75,000,000
Available-for-sale securities, gross unrealized gain (loss)       0 0
Convertible Notes, face amount 258,800,000        
Estimated fair value of the debt     289,800,000    
Convertible Notes, trading price   $ 1,120