Loss Per Share and Stockholders' Equity (Cost of Shares Retired) (Details) $ in Thousands	9 Months Ended
	Jan. 31, 2018 USD ($)
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	$ 109,406
Common stock
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	47
Additional paid-in-capital
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	2,818
Retained earnings
Equity, Class of Treasury Stock [Line Items]
Shares retired during year, value	$ 106,541