Credit Agreement - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Jul. 31, 2011	Jan. 31, 2011
Line of Credit Facility [Line Items]
Revolving credit facility, available credit	$ 500	$ 300
Revolving credit facility, permitted carry over of capital expenditure limitation	10.0
Revolving credit facility, capital expenditure limitation with the permitted carry over	70.0
Revolving credit facility, right	one-time right, at any time during the Company’s fiscal year ending October 31, 2011 or October 31, 2012, to increase the maximum debt to total capitalization ratio then in effect by 5% for the four fiscal quarters beginning on the first day of the fiscal quarter during which the Company gives written notice of its intent to exercise this right
Revolving credit facility, expiration date	2016-02-23
Revolving credit facility, outstanding borrowings	182.7
Borrowings on Revolving Credit Facility
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding borrowings	182.7
Revolving credit facility, amount available	307.7
Fiscal Year 2011
Line of Credit Facility [Line Items]
Revolving credit facility, capital expenditure limitation	60
Fiscal Years 2012 Through 2015
Line of Credit Facility [Line Items]
Revolving credit facility, capital expenditure limitation	55
February 23, 2011 Through October 30, 2014
Line of Credit Facility [Line Items]
Revolving credit facility, maximum debt to total capitalization ratio	55.00%
Thereafter October 30, 2014
Line of Credit Facility [Line Items]
Revolving credit facility, maximum debt to total capitalization ratio	50.00%
Letter of Credit
Line of Credit Facility [Line Items]
Revolving credit facility, outstanding borrowings	9.6
Construction Loans
Line of Credit Facility [Line Items]
Revolving credit facility, capital expenditure limitation	$ 115