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Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Jan. 31, 2015	Jan. 31, 2016	Apr. 30, 2015
Income Tax Contingency
Unrecognized tax benefits		$ 9,055	$ 8,043
Unrecognized tax benefits that would impact effective tax rate		5,923
Accrued interest and penalties related to unrecognized tax benefits		338	$ 152
Interest and penalties included in income tax expense	$ (176)	186
Expected decrease in unrecognized tax benefits		$ 2,942
Federal Tax Authority \| Earliest Tax Year
Income Tax Contingency
Tax years open for examination		2012
State Tax Authority \| Earliest Tax Year
Income Tax Contingency
Tax years open for examination		2010
Illinois \| Tax Year 2011
Income Tax Contingency
Year under examination		2011
Illinois \| Tax Year 2012
Income Tax Contingency
Year under examination		2012