Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2019	Apr. 30, 2018
Deferred tax assets:
Accrued liabilities and reserves	$ 11,705	$ 7,978
Property and equipment depreciation	24,661	24,419
Workers compensation	8,277	7,244
Deferred compensation	3,827	3,846
Equity compensation	6,727	7,158
Federal net operating losses	0	2,769
State net operating losses & tax credits	775	2,336
Other	1,033	889
Total gross deferred tax assets	57,005	56,639
Less valuation allowance	47	47
Total net deferred tax assets	56,958	56,592
Deferred tax liabilities:
Property and equipment depreciation	(420,710)	(378,756)
Goodwill	(21,560)	(19,548)
Other	(476)	(234)
Total gross deferred tax liabilities	(442,746)	(398,538)
Net deferred tax liability	$ (385,788)	$ (341,946)