Loss Per Share and Stockholders' Equity (Cost of Shares Retired) (Details) $ in Thousands	6 Months Ended
	Oct. 31, 2017 USD ($)
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	$ 97,105
Common stock
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	42
Additional paid-in-capital
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	2,503
Retained earnings
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	$ 94,560