Leases - Components of Lease Costs (Details) - USD ($)	12 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Lease, Cost [Abstract]
Reduction in the carrying value of right-of-use assets	$ 635,000	$ 2,582,000
Interest on lease liabilities	73,000	205,000
Operating lease cost	27,192,000	25,405,000
Operating cash flows for finance leases	73,000	205,000
Operating cash flows for operating leases	24,371,000	22,595,000
Financing cash flows for financing leases	608,000	2,512,000
Right-of-use assets obtained in exchange for new finance lease liabilities	2,222	1,650
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 8,914	$ 72,703
Weighted average remaining lease term - finance leases	2 years 11 months 12 days	3 years 4 months 9 days
Weighted average remaining lease term - operating leases	6 years 7 months 13 days	7 years 4 months 28 days
Weighted average discount rate - finance leases (percent)	2.95%	3.19%
Weighted average discount rate - operating leases (percent)	3.23%	4.27%