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Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)
 9 Months Ended
Sep. 30, 2013
Sep. 30, 2012
Derivative [Line Items]    
U.S. Treasury Note, maturity term (in years) 10 years  
Proceeds from or (payments to) settlement of interest rate protection agreement   $ 65,500,000
Net amount of settlement gains (losses) on derivative instruments included in accumulated OCI to be amortized over next 12 months, before tax (5,700,000)  
Net amount of settlement gains (losses) on derivative instruments included in accumulated OCI to be amortized over next 12 months, after tax (3,700,000)  
2008 Interest Rate Protection Agreement
    
Derivative [Line Items]    
Proceeds from or (payments to) settlement of interest rate protection agreement (4,400,000)  
2010 Interest Rate Protection Agreement
    
Derivative [Line Items]    
Proceeds from or (payments to) settlement of interest rate protection agreement 9,900,000  
2011 Interest Rate Protection Agreement
    
Derivative [Line Items]    
Proceeds from or (payments to) settlement of interest rate protection agreement $ (65,500,000)