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Recent Accounting Standards (Details) - USD ($)
$ in Millions
 3 Months Ended
Jul. 31, 2017
Jul. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Increase (decrease) in diluted shares outstanding (in shares) 693,000 738,000
Accounting Standards Update 2017-07 Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Net benefit costs expected to be reclassified from operating income to a line item below operating income $ 1.9 $ 0.8
Accounting Standards Update 2016-09 [Member]    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]    
Excess income tax benefits from stock-based compensation $ 0.2  
Increase (decrease) in diluted shares outstanding (in shares) 11,000  
Excess tax benefits recorded in operating activities $ 0.2  
Excess tax benefits recorded in financing activities   $ 0.3