Treasury Stock and Repurchase Program - Components of treasury stock, at cost (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended						9 Months Ended
		Jan. 31, 2016		Oct. 31, 2015		Jul. 31, 2015		Jan. 31, 2016	Jan. 31, 2015
Shares
Balance as of April 30, 2015	[1],[2]					190,504		190,504
Purchases effected in open market (in shares)	[2]	4,118		25,098		12,237
Balance as of January 31, 2016		231,957						231,957
Total Average Cost Assigned
Balance as of April 30, 2015	[1],[2]					$ 2,244		$ 2,244
Purchases effected in open market		$ 61	[2]	$ 382	[2]	$ 166	[2]	609	$ 71
Balance as of January 31, 2016		$ 2,853						$ 2,853
Average Cost per Share
Balance as of April 30, 2014	[1],[2]					$ 11.78		$ 11.78
Purchases effected in open market	[2]	$ 14.74		$ 15.23		$ 13.58
Balance as of January 31, 2016		$ 12.30						$ 12.30
Aggregate Purchase Price Remaining Under the Program
Balance as of April 30, 2015	[1],[2]					$ 2,146		$ 2,146
Purchases effected in open market	[2]	$ 1,537		$ 1,598		$ 1,980		1,537
Balance as of January 31, 2016		$ 1,537						$ 1,537

[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.