Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2018	Apr. 30, 2017
Deferred tax assets:
Accrued liabilities and reserves	$ 7,978	$ 10,948
Property and equipment depreciation	24,419	16,604
Workers compensation	7,244	10,934
Deferred compensation	3,846	5,916
Equity compensation	7,158	6,923
Federal net operating losses	2,769	0
State net operating losses & tax credits	2,336	938
Other	889	1,275
Total gross deferred tax assets	56,639	53,538
Less valuation allowance	47	60
Total net deferred tax assets	56,592	53,478
Deferred tax liabilities:
Property and equipment depreciation	(378,756)	(468,470)
Goodwill	(19,548)	(25,052)
Other	(234)	(80)
Total gross deferred tax liabilities	(398,538)	(493,602)
Net deferred tax liability	$ (341,946)	$ (440,124)