Significant Assumptions Used to Determine Fair Value of Auction Rate Securities (Detail)	Apr. 30, 2013	Oct. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Yields	2.15%	2.15%
Libor plus stated yield	2.00%	2.00%
Minimum
Schedule of Available-for-sale Securities [Line Items]
Libor plus the stated discount rate	0.44%	1.37%
Average expected lives	4	4
Maximum
Schedule of Available-for-sale Securities [Line Items]
Libor plus the stated discount rate	3.43%	6.86%
Libor plus stated yield		3.50%
Average expected lives	10	10