Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	3 Months Ended
	Jul. 31, 2015	Jul. 31, 2014	Apr. 30, 2015
Income Tax Contingency
Unrecognized tax benefits	$ 8,472		$ 8,043
Unrecognized tax benefits that would impact effective tax rate	5,544
Accrued interest and penalties related to unrecognized tax benefits	271		$ 152
Interest and penalties included in income tax expense	119	$ (213)
Expected decrease in unrecognized tax benefits	$ 2,993
Federal Tax Authority | Earliest Tax Year
Income Tax Contingency
Tax years open for examination	2011
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