Federal, State and Local Income Taxes - Provision for income taxes (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2015	Jan. 31, 2014
Current tax expense:
Federal	$ 716us-gaap_CurrentFederalTaxExpenseBenefit	$ 949us-gaap_CurrentFederalTaxExpenseBenefit	$ 2,668us-gaap_CurrentFederalTaxExpenseBenefit	$ 2,003us-gaap_CurrentFederalTaxExpenseBenefit
State and local	9	66	161	140
Current tax expense	725us-gaap_CurrentIncomeTaxExpenseBenefit	1,015us-gaap_CurrentIncomeTaxExpenseBenefit	2,829us-gaap_CurrentIncomeTaxExpenseBenefit	2,143us-gaap_CurrentIncomeTaxExpenseBenefit
Deferred tax expense:
Federal	198	(9)	198	521
State and local	(129)	20	(65)	111
Deferred tax expense	69us-gaap_DeferredIncomeTaxExpenseBenefit	11us-gaap_DeferredIncomeTaxExpenseBenefit	133us-gaap_DeferredIncomeTaxExpenseBenefit	632us-gaap_DeferredIncomeTaxExpenseBenefit
Income tax provision:	$ 794us-gaap_IncomeTaxExpenseBenefit	$ 1,026us-gaap_IncomeTaxExpenseBenefit	$ 2,962us-gaap_IncomeTaxExpenseBenefit	$ 2,775us-gaap_IncomeTaxExpenseBenefit

Amount of current federal tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of current income tax expense (benefit) pertaining to taxable income (loss) from continuing operations.

Amount of current state and local tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred federal income tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred income tax expense (benefit) pertaining to income (loss) from continuing operations.

Amount of deferred state and local tax expense (benefit) pertaining to income (loss) from continuing operations.