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Credit Facilities - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
1 Months Ended
Sep. 30, 2011
Amendment
Revolving Credit Agreement
Sep. 30, 2011
Revolving Credit Agreement
Jul. 05, 2011
Senior Unsecured Notes, 3.75 Percent, Due April 27th, 2018
Line of Credit Facility [Line Items]   
Aggregate principal amount under revolving credit agreements$ 150.0$ 60.0 
Senior unsecured notes, aggregate principal amount  125
Senior unsecured notes, interest rate  3.75%
Senior unsecured notes, maturity dateApr. 27, 2018
Senior unsecured notes, date of first required interest paymentJul. 27, 2011
Senior unsecured notes, required principal payments  $ 25
Senior unsecured notes, date of first required principal paymentsApr. 27, 2014