Treasury Stock and Repurchase Program - Components of treasury stock, at cost (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended			6 Months Ended
	Oct. 31, 2013	Jul. 31, 2013		Oct. 31, 2013		Oct. 31, 2012
Shares
Balance as of April 30, 2013		123,572	[1],[2],[3]	123,572	[1],[2],[3]
Purchases effected in open market	13,428	25,723
Balance as of October 31, 2013	162,723			162,723
Total Average Cost Assigned
Balance as of April 30, 2013		$ 1,572	[1],[2],[3]	$ 1,572	[1],[2],[3]
Purchases effected in open market	123	226		349		30
Balance as of October 31, 2013	1,921			1,921
Average Cost per Share
Balance as of April 30, 2013		$ 12.72	[1],[2],[3]	$ 12.72	[1],[2],[3]
Purchases effected in open market	$ 9.13	$ 8.82
Balance as of October 31, 2013	$ 11.81			$ 11.81
Aggregate Purchase Price Remaining Under the Program
Balance as of April 30, 2013		2,818	[1],[2],[3]	2,818	[1],[2],[3]
Purchases effected in open market	$ 2,469	$ 2,592

[1] Includes 18,400 shares with a total average cost of $354,000 that were acquired prior to the repurchase program authorized in January 2011.

[2] 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.

[3] Includes 19,953 shares with a total average cost of $182,000 that were acquired during the new repurchase program authorized in September 2012.