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Risk Management and Derivative Financial Instruments - Additional Information (Detail)
Aug. 15, 2012
USD ($)
Derivative [Line Items]  
Liquidation of interest rate swap agreement $ 42,700,000
Interest Rate Cash Flow Hedges  
Derivative [Line Items]  
Amount of debt hedged 200,000,000
3.40% Senior Notes due 2022 | Senior Notes  
Derivative [Line Items]  
Aggregate principal of Senior Notes $ 300,000,000
Debt instrument term 10 years
Interest rate on Senior Notes 3.40%