New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016	Apr. 30, 2017
Accounting Changes and Error Corrections [Abstract]
Excess tax benefit related to stock-based compensation
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification from operating activities			$ (41,838)	$ (40,146)
Reclassification to financing activities			$ (25,135)	$ (8,548)
Basic (in usd per share)	$ 1.22	$ 1.08	$ 2.59	$ 2.41
Diluted (in usd per share)	$ 1.21	$ 1.07	$ 2.58	$ 2.39
Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification to financing activities				$ 2,600
Accounting Standards Update 2015-03 [Member] | Long-term Debt [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of debt issuance costs					$ 300