Notes Payable - Redemption Prices Expressed as a Percentage of Principal, Plus any Accrued and Unpaid Interest (Detail)	Jul. 31, 2012
Debt Instrument [Line Items]
Redemption Price	100.00%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Redemption Period Beginning on April 5, 2016 and ending on March 31, 2017
Debt Instrument [Line Items]
Redemption Price	101.143%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Redemption Period Beginning on April 1, 2017 and ending on March 31, 2018
Debt Instrument [Line Items]
Redemption Price	100.571%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Redemption Period On April 1, 2018 and thereafter
Debt Instrument [Line Items]
Redemption Price	100.00%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Holder Optional Redemption Period 1 [Member]
Debt Instrument [Line Items]
Redemption Price	100.00%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Holder Optional Redemption Period 2 [Member]
Debt Instrument [Line Items]
Redemption Price	100.00%
4.00% Debentures due 2031 | Convertible Subordinated Debt | Holder Optional Redemption Period 3 [Member]
Debt Instrument [Line Items]
Redemption Price	100.00%