Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Apr. 30, 2015	Apr. 30, 2014
Deferred tax assets
Accrued liabilities and reserves	$ 8,593	$ 16,830
Property and equipment depreciation	12,846	11,788
Workers compensation	9,536	8,501
Deferred compensation	6,653	6,272
Equity compensation	3,767	3,598
State net operating losses & tax credits	626	2,757
Other	1,787	3,265
Total gross deferred tax assets	43,808	53,011
Less valuation allowance	228	0
Total net deferred tax assets	43,580	53,011
Deferred tax liabilities
Property and equipment depreciation	(363,965)	(332,095)
Goodwill	(18,319)	(14,989)
Other	(738)	(658)
Total gross deferred tax liabilities	(383,022)	(347,742)
Net deferred tax liability	$ (339,442)	$ (294,731)