Treasury Stock and Repurchase Program - Components of treasury stock, at cost (Details) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013		Apr. 30, 2012
Treasury Stock At Cost [Roll Forward]
Balance (in shares)		182,071	123,572	103,619	[1]
Purchases effected in open market, shares	[2]	8,433	58,499	19,953
Balance (in shares)		190,504	182,071	123,572
Total Average Cost Assigned, Beginning Balance (in dollars)		$ 2,122	$ 1,572	$ 1,390	[1]
Purchases effected in open market (in dollars)	[2]	122	550	182
Total Average Cost Assigned, Ending Balance (in dollars)		$ 2,244	$ 2,122	$ 1,572
Average Cost per Share, Beginning Balance (in dollars per share)		$ 11.65	$ 12.72	$ 13.41	[1]
Average cost per share	[2]	14.47	9.41	9.13
Average Cost per Share, Ending Balance (in dollars per share)		$ 11.78	$ 11.65	$ 12.72
Aggregate purchase price remaining under the program		$ 2,146	$ 2,268	$ 2,818

[1] Includes 85,219 shares with a total average cost of $1,036,000 that were acquired during the former repurchase program, which was authorized in January 2011 and expired in January 2012; 18,400 shares were acquired prior to the repurchase program authorized in January 2011.

[2] Were acquired during the $3 million repurchase program authorized in September 2012.