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Income Tax Expense (Details)
 3 Months Ended 12 Months Ended
Mar. 31, 2018
USD ($)
Partnership
Mar. 31, 2017
USD ($)
Dec. 31, 2017
USD ($)
Partnership
Income Tax Expense [Abstract]      
Number of investments in partnerships | Partnership 4   4
Investment amount in partnerships $ 514,000   $ 541,000
Investment Tax Credit Carryforward [Member]      
Tax Credit Carryforward [Line Items]      
Investment tax credits $ 670,000    
Tax credits recognition period 4 years 9 months    
Tax credits recognized as reduction of tax expense amount $ 35,000 $ 35,000  
Amortization of investments in other expenses $ 27,000 $ 40,000