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Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)
 6 Months Ended
Jun. 30, 2012
Year
Jun. 30, 2011
Derivative [Line Items]    
U.S. Treasury Note, maturity term (in years) 10  
(Proceeds from) or payments to settlement of interest rate protection agreement $ (65,500,000) $ 9,910,000
Foreign currency forward contracts settled for a loss, amount 700,000  
Number of foreign currency forward contracts outstanding 0  
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain amortized 3,300,000  
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain realized after tax 2,100,000  
Ineffective portion of derivative instruments 3,400,000  
Interest Rate Contract
    
Derivative [Line Items]    
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain amortized 2,200,000  
Net amount of settlement gains or losses on derivative instruments included in accumulated OCI, net gain realized after tax 1,400,000  
Two Thousand And Three Interest Rate Protection Agreement
    
Derivative [Line Items]    
(Proceeds from) or payments to settlement of interest rate protection agreement 22,800,000  
Two Thousand And Eight Interest Rate Protection Agreement
    
Derivative [Line Items]    
(Proceeds from) or payments to settlement of interest rate protection agreement 4,400,000  
Two Thousand And Ten Interest Rate Protection Agreement
    
Derivative [Line Items]    
(Proceeds from) or payments to settlement of interest rate protection agreement 9,900,000  
Two Thousand And Eleven Interest Rate Protection Agreement
    
Derivative [Line Items]    
(Proceeds from) or payments to settlement of interest rate protection agreement $ 65,500,000