New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015	Apr. 30, 2016
Accounting Changes and Error Corrections [Abstract]
Excess tax benefit related to stock-based compensation			$ 1,200
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification from operating activities			(40,146)	$ (41,988)
Reclassification to financing activities			$ (8,548)	$ (762)
Basic (in usd per share)	$ 1.08	$ 1.12	$ 2.41	$ 2.05
Diluted (in usd per share)	$ 1.07	$ 1.10	$ 2.39	$ 2.03
Accounting Standards Update 2016-09 [Member] | New Accounting Pronouncement, Early Adoption, Effect [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification from operating activities		$ 2,600
Reclassification to financing activities		$ 2,600
Accounting Standards Update 2015-03 [Member] | Other Noncurrent Assets [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of debt issuance costs					$ (300)
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