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Dividends (Details) (USD $)
3 Months Ended 6 Months Ended 0 Months Ended
Mar. 28, 2015
Mar. 29, 2014
Mar. 28, 2015
Mar. 29, 2014
Oct. 23, 2014
Jan. 22, 2015
Class A Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock $ 0.165us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.165us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.33us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.33us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
   
Class B Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock $ 0.150us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 0.150us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 0.30us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 0.30us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
   
Dividend 1 [Member]            
Dividends Payable [Line Items]            
Dividend payment date     Oct. 23, 2014      
Dividend record date     Oct. 09, 2014      
Dividend 1 [Member] | Class A Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock         $ 0.165us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= imkta_Dividend1Member
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
 
Dividend 1 [Member] | Class B Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock         $ 0.15us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= imkta_Dividend1Member
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
 
Dividend 2 [Member]            
Dividends Payable [Line Items]            
Dividend payment date     Jan. 22, 2015      
Dividend record date     Jan. 08, 2015      
Dividend 2 [Member] | Class A Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock           $ 0.165us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= imkta_Dividend2Member
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Dividend 2 [Member] | Class B Common Stock [Member]            
Dividends Payable [Line Items]            
Cash dividends per share of common stock           $ 0.15us-gaap_CommonStockDividendsPerShareCashPaid
/ us-gaap_DividendsAxis
= imkta_Dividend2Member
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember