Stock Repurchase Program - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended			3 Months Ended			9 Months Ended
	May 25, 2011	Jul. 31, 2011	Jul. 31, 2012		Jul. 31, 2011	Apr. 30, 2012 Accelerated Share Repurchase Agreement	Jan. 31, 2012 Accelerated Share Repurchase Agreement	Oct. 31, 2011 Accelerated Share Repurchase Agreement	Jul. 31, 2012 Accelerated Share Repurchase Agreement	Jan. 06, 2012 Accelerated Share Repurchase Agreement	Sep. 30, 2011 Accelerated Share Repurchase Agreement
Stock Repurchase Program [Line Items]
Stock repurchase program authorized amount	$ 500.0		$ 500.0
Stock repurchase program remaining authorized repurchase amount			272.4
Accelerated share repurchase agreement amount										40.0	75.0
Stock repurchase program prepayment										40.0	75.0
Initial number of shares received from accelerated share repurchase agreements							744,325	1,710,376
Initial share value							20.0	41.7
Remaining balance of value or shares to be settled							$ 20.0	$ 33.3
Number of shares to settle equity forward contract						624,291	1,105,457
Average purchase price per share		$ 26.11	$ 29.64	[1]	$ 26.93		$ 26.64		$ 29.23
Additional accelerated share repurchase agreement entered date							Jan. 06, 2012

[1] Amount includes $33.3 million from the settlement of the September 2011 ASR equity forward contract.