Federal, State and Local Income Taxes - Provision for income taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2016	Jan. 31, 2015
Current tax expense:
Federal	$ 906	$ 716	$ 2,916	$ 2,668
State and local	62	9	189	161
Current tax expense	968	725	3,105	2,829
Deferred tax expense (benefit):
Federal	(271)	198	(449)	198
State and local	(1)	(129)	(222)	(65)
Deferred tax expense (benefit):	(272)	69	(671)	133
Income tax provision	$ 696	$ 794	$ 2,434	$ 2,962