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Stock-Based Compensation - Stock Option Assumptions (Detail) (USD $)
1 Months Ended 12 Months Ended 6 Months Ended
Sep. 30, 2012
Jul. 31, 2008
Jan. 31, 2013
Service Based Option [Member]
Jan. 31, 2012
Service Based Option [Member]
Jan. 31, 2012
Performance Based Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Expected term     5 years 11 months 12 days 5 years 10 months 21 days 6 years 6 months 26 days
Expected volatility     38.68% 39.40% 39.21%
Expected dividend yield     2.20% 2.07% 1.99%
Risk-free interest rate     0.90% 1.16% 2.05%
Weighted-average market value of underlying stock at grant date (USD per share)     $ 30.36 $ 27.00 $ 29.55
Weighted average exercise price (USD per share) $ 30.21 $ 32.83 $ 30.36 $ 27.00 $ 29.55
Weighted-average fair value of options granted during the period (USD per share) $ 30.21 $ 32.83 $ 9.01 $ 8.37 $ 10.01