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Other Financial Instruments and Fair Value Measurements (Details Textual) - USD ($)
$ in Millions
 12 Months Ended
Apr. 30, 2015
Mar. 20, 2015
Feb. 02, 2015
Apr. 30, 2014
Other Financial Instruments and Fair Value Measurements (Textual) [Abstract]        
Company's Municipal bond mature in 2016 $ 0.9      
Company's Municipal bond mature in 2017 1.3      
Company's Municipal bond mature in 2018 1.1      
Company's Municipal bond mature in 2019 3.0      
Company's Municipal bond mature in 2020 and beyond $ 31.6      
Money market funds maturity period Three months of less      
Debt Instrument, Face Amount   $ 3,700.0    
Interest rate contract [Member]        
Derivative Instruments, Gain (Loss) [Line Items]        
Gross contract notional amount $ 0.0   $ 1,100.0 $ 750.0