Consolidated Balance Sheets (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Jul. 31, 2016	Jul. 31, 2015	Apr. 30, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 3.4		$ 2.1
Redeemable convertible preferred stock, par value (in US$ per share)	$ 0.0001		$ 0.0001
Redeemable convertible preferred stock, authorized (shares)	6,000,000		6,000,000
Redeemable convertible preferred stock, issued (shares)	671,189		671,189
Cumulative preferred dividends in arrears	$ 7.9	$ 7.1
Common stock, par value (in US$ per share)	$ 0.003		$ 0.003
Common stock, authorized (shares)	544,000,000		544,000,000
Capital stock, issued (shares)	2,721,837		2,721,592