Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2017	Apr. 30, 2016
Deferred tax assets
Accrued liabilities and reserves	$ 10,948	$ 11,522
Property and equipment depreciation	16,604	15,914
Workers compensation	10,934	10,540
Deferred compensation	5,916	6,696
Equity compensation	6,923	5,186
State net operating losses & tax credits	938	973
Other	1,275	1,582
Total gross deferred tax assets	53,538	52,413
Less valuation allowance	60	84
Total net deferred tax assets	53,478	52,329
Deferred tax liabilities
Property and equipment depreciation	(468,470)	(425,586)
Goodwill	(25,052)	(21,677)
Other	(80)	0
Total gross deferred tax liabilities	(493,602)	(447,263)
Net deferred tax liability	$ (440,124)	$ (394,934)