Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2020	Apr. 30, 2019
Deferred tax assets:
Accrued liabilities and reserves	$ 15,953	$ 11,705
Property and equipment depreciation	27,512	24,661
Workers compensation	8,303	8,277
Deferred compensation	3,781	3,827
Equity compensation	7,083	6,727
State net operating losses & tax credits	424	775
Other	1,335	1,033
Total gross deferred tax assets	64,391	57,005
Less valuation allowance	47	47
Total net deferred tax assets	64,344	56,958
Deferred tax liabilities:
Property and equipment depreciation	(474,829)	(420,710)
Goodwill	(24,348)	(21,560)
Other	(765)	(476)
Total gross deferred tax liabilities	(499,942)	(442,746)
Net deferred tax liability	$ (435,598)	$ (385,788)