Treasury Stock and Repurchase Program - Components of treasury stock, at cost (Parentheticals) (Details) - USD ($)		1 Months Ended		3 Months Ended						9 Months Ended
		Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2016		Oct. 31, 2015		Jul. 31, 2015		Jan. 31, 2016	Jan. 31, 2015	Sep. 19, 2012
Equity, Class of Treasury Stock [Line Items]
Number of treasury shares (in shares)	[1]			4,118		25,098		12,237
Total average cost				$ 61,000	[1]	$ 382,000	[1]	$ 166,000	[1]	$ 609,000	$ 71,000
September 2012 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Authorized repurchase amount of common stock												$ 3,000,000
January 2011 Share Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Number of treasury shares (in shares)			18,400
Former Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Number of treasury shares (in shares)		85,219
Total average cost		$ 1,036,000

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