Quarterly report pursuant to Section 13 or 15(d)

Fair Value of Employee Stock Options Granted as Determined by Black-Scholes Valuation Model Assumptions (Detail)

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Fair Value of Employee Stock Options Granted as Determined by Black-Scholes Valuation Model Assumptions (Detail) (Nonqualified Stock Options [Member])
3 Months Ended
Mar. 31, 2012
Y
Sep. 30, 2011
Y
Nonqualified Stock Options [Member]
   
Stockholders Equity Note [Line Items]    
Expected life (in years) 7.5 7.5
Risk-free interest rate 1.63% 2.90%
Expected volatility 25.06% 24.26%
Expected dividend yield 2.77% 2.77%