Restructuring Charges - Accrued Liability Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Oct. 31, 2017	Oct. 31, 2016	Oct. 31, 2017	Oct. 31, 2016
Restructuring Cost and Reserve [Line Items]
Balance at April 30, 2016			$ 1,407	$ 1,043
Restructuring charges	$ 16	$ 767	56	1,094
Payments			(1,191)	(1,766)
Non-cash settlements of restructuring charges			(46)
Balance at October 31, 2017	226	371	226	371
Employee Severance [Member]
Restructuring Cost and Reserve [Line Items]
Balance at April 30, 2016			1,108	497
Restructuring charges			56	459
Payments			(1,164)	(929)
Non-cash settlements of restructuring charges			0
Balance at October 31, 2017	0	27	0	27
Other Restructuring [Member]
Restructuring Cost and Reserve [Line Items]
Balance at April 30, 2016			299	546
Restructuring charges			0	635
Payments			(27)	(837)
Non-cash settlements of restructuring charges			(46)
Balance at October 31, 2017	$ 226	$ 344	$ 226	$ 344