Acquisitions - Unaudited Pro Forma Financial Information (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Jan. 31, 2015		Jan. 31, 2014
Business Combinations [Abstract]
Total revenues	$ 6,128,936		$ 6,016,403
Net earnings	$ 139,471	[1]	$ 107,118	[1]
Earnings per common share: (1)
Basic (in dollars per share)	$ 3.60	[1]	$ 2.79	[1]
Diluted (in dollars per share)	$ 3.58	[1]	$ 2.76	[1]

[1] Due to the revision of the financial statements described in the Form 10-K/A (Amendment No. 1) filed on December 10, 2014, net earnings and earnings per common share for the nine months ended January 31, 2014 have been revised.