Goodwill - Additional Information (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	$ 139,155,000	$ 139,155,000	$ 132,831,000
Goodwill impairment	$ 0	$ 0