Changes in Each Component of Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands		12 Months Ended
		Apr. 30, 2016	Apr. 30, 2015	Apr. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance		$ (40,623)	$ (2,388)	$ (2,631)
Unrealized (losses) gains arising during the period		(19,077)	(40,122)	(1,883)
Reclassification of realized net losses to net income		1,789	1,887	2,126
Accumulated other comprehensive (loss) income, ending balance		(57,911)	(40,623)	(2,388)
Accumulated Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance		(20,919)	15,604	17,559
Unrealized (losses) gains arising during the period		(15,420)	(36,523)	(1,955)
Accumulated other comprehensive (loss) income, ending balance		(36,339)	(20,919)	15,604
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance	[1]	(19,708)	(18,006)	(20,236)
Unrealized (losses) gains arising during the period	[1]	(3,653)	(3,589)	136
Reclassification of realized net losses to net income	[1]	1,789	1,887	2,094
Accumulated other comprehensive (loss) income, ending balance	[1]	(21,572)	(19,708)	(18,006)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive (loss) income, beginning balance		4	14	46
Unrealized (losses) gains arising during the period		$ (4)	(10)	(64)
Reclassification of realized net losses to net income				32
Accumulated other comprehensive (loss) income, ending balance			$ 4	$ 14

[1] The tax effects on unrealized (losses) gains were $(2.3) million, $(2.3) million and $0.07 million as of April 30, 2016, 2015 and 2014, respectively. The tax effects on reclassifications of realized net losses were $1.1 million, $1.2 million and $1.0 million as of April 30, 2016, 2015 and 2014, respectively.