Changes in Each Component of Accumulated Other Comprehensive (Loss) Income (Parenthetical) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Tax effects on unrealized (losses) gains	$ (2,300)	$ (2,300)	$ 70
Tax effects on reclassifications of realized net losses	$ 1,100	$ 1,200	$ 1,000