Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2016	Apr. 30, 2015
Deferred tax assets
Accrued liabilities and reserves	$ 11,522	$ 8,593
Property and equipment depreciation	15,914	12,846
Workers compensation	10,540	9,536
Deferred compensation	6,696	6,653
Equity compensation	5,186	3,767
State net operating losses & tax credits	973	626
Other	1,582	1,787
Total gross deferred tax assets	52,413	43,808
Less valuation allowance	84	228
Total net deferred tax assets	52,329	43,580
Deferred tax liabilities
Property and equipment depreciation	(425,586)	(363,965)
Goodwill	(21,677)	(18,319)
Other	0	(738)
Total gross deferred tax liabilities	(447,263)	(383,022)
Net deferred tax liability	$ (394,934)	$ (339,442)