Stock-Based Compensation Restricted Stock Awards (Details)	12 Months Ended
	Apr. 30, 2022 $ / shares shares
Restricted stock awards | 2021 Plan
Shares
Stock granted (in shares) | shares	47,026
Stock canceled (in shares) | shares	(1,950)
Unvested stock at end of year (in shares) | shares	45,076
Weighted Average Grant Date Fair Value
Stock granted (in dollars per shares) | $ / shares	$ 75.66
Stock canceled (in dollars per shares) | $ / shares	74.27
Unvested stock at end of year (in dollars per share) | $ / shares	$ 75.71
Restricted stock awards | Restated 2006 Plan
Shares
Unvested stock at beginning of year (in shares) | shares	180,028
Stock granted (in shares) | shares	57,376
Stock vested (in shares) | shares	(94,389)
Stock canceled (in shares) | shares	(30,170)
Unvested stock at end of year (in shares) | shares	112,845
Weighted Average Grant Date Fair Value
Unvested stock at beginning of year (in dollars per share) | $ / shares	$ 83.02
Stock granted (in dollars per shares) | $ / shares	66.10
Stock vested (in dollars per shares) | $ / shares	62.52
Stock canceled (in dollars per shares) | $ / shares	89.58
Unvested stock at end of year (in dollars per share) | $ / shares	$ 89.80
Restricted stock units | Restated 2006 Plan
Shares
Stock granted (in shares) | shares	4,395
Unvested stock at end of year (in shares) | shares	4,395
Weighted Average Grant Date Fair Value
Stock granted (in dollars per shares) | $ / shares	$ 97.96
Unvested stock at end of year (in dollars per share) | $ / shares	$ 97.69