New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Apr. 30, 2016
Accounting Changes and Error Corrections [Abstract]
Excess tax benefit related to stock-based compensation			$ 1,300
New Accounting Pronouncement, Early Adoption [Line Items]
Reclassification from operating activities			(51,664)	$ (53,561)
Reclassification to financing activities			$ (11,177)	$ (4,744)
Basic (in usd per share)	$ 0.90	$ 0.74	$ 3.31	$ 2.79
Diluted (in usd per share)	$ 0.89	$ 0.73	$ 3.28	$ 2.76
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