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Income Taxes (Details 5) (USD $)
In Thousands, unless otherwise specified
12 Months Ended
Apr. 26, 2015
Apr. 27, 2014
Apr. 28, 2013
Reconciliation of the beginning and ending amounts of unrecognized tax benefits      
Beginning Balance   $ 4,072us-gaap_UnrecognizedTaxBenefits $ 4,072us-gaap_UnrecognizedTaxBenefits
Impact of favorable court ruling   (4,072)us-gaap_UnrecognizedTaxBenefitsDecreasesResultingFromSettlementsWithTaxingAuthorities  
Ending Balance     4,072us-gaap_UnrecognizedTaxBenefits
Additional information related to unrecognized tax benefits      
Portion of benefits recognized, that affect the effective tax rate, principal amount   4,072isle_UnrecognizedTaxBenefitsThatImpactEffectiveTaxRatePrincipleAmount  
Portion of benefits recognized, that affect the effective tax rate, interest amount   4,025isle_UnrecognizedTaxBenefitsThatImpactEffectiveTaxRateInterestAmount  
Interest expense related to prior periods unrecognized tax benefits 0us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense 390us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense 466us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesExpense
Accrued interest recognized related to the unrecognized tax benefits     3,635us-gaap_UnrecognizedTaxBenefitsInterestOnIncomeTaxesAccrued
Accrued penalties related to the unrecognized tax benefits $ 0us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued $ 0us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued $ 0us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAccrued