Stock-based Compensation - Summary of Stock Options (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Apr. 30, 2016 USD ($) $ / shares shares
Number of Options
Beginning balance (in shares) | shares	338
Granted (in shares) | shares	923
Exercised (in shares) | shares	(87)
Canceled (in shares) | shares	(64)
Ending balance (in shares) | shares	1,110
Vested or expected to vest at end of year (in shares) | shares	1,046
Exercisable at end of year (in shares) | shares	49
Weighted- Average Exercise Price
Beginning balance (in usd per share) | $ / shares	$ 36.22
Granted (in usd per share) | $ / shares	55.39
Exercised (in usd per share) | $ / shares	36.49
Canceled (in usd per share) | $ / shares	39.03
Ending balance (in usd per share) | $ / shares	52.09
Vested or expected to vest at end of year (in usd per share) | $ / shares	52.17
Exercisable at end of year (in usd per share) | $ / shares	$ 35.22
Aggregate Intrinsic Value
Balance at end of year | $	$ 1,402
Vested or expected to vest at end of year | $	1,279
Exercisable at end of year | $	$ 402