| 
           Stock Repurchase Programs (Details) (USD $) 
        In Millions, except Share data, unless otherwise specified  | 
        6 Months Ended | 12 Months Ended | 1 Months Ended | ||
|---|---|---|---|---|---|
| 
           Mar. 31, 2012 
         | 
        
           Mar. 31, 2012
 
          2008 and 2010 Plan 
         | 
        
           Mar. 31, 2011
 
          2008 and 2010 Plan 
         | 
        
           Sep. 30, 2010
 
          2008 and 2010 Plan 
         | 
        
           Nov. 30, 2011
 
          2011 Plan 
         | 
      |
| Stock Repurchase Programs | |||||
| Stock repurchase programs, authorized amount | $ 175.0 | $ 125.0 | |||
| Common shares repurchased | 236,700 | 275,158 | |||
| Common shares repurchased, cost | 8.8 | 8.5 | |||
| Amount remaining available for future stock repurchases | $ 129.8 | ||||
| X | ||||||||||
| 
             
- Details 
          
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The amount authorized by an entity's Board of Directors under a stock repurchase plan. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          The remaining repurchase amount authorized by an entity's Board of Directors under a stock repurchase plan. No definition available. 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Number of shares that have been repurchased during the period and are being held in treasury. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  | 
        
| X | ||||||||||
| 
             
- Definition 
          Equity impact of the cost of common and preferred stock that were repurchased during the period. Recorded using the cost method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
  |