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Income Tax Expense (Details)
 3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2017
USD ($)
Jun. 30, 2016
USD ($)
Jun. 30, 2017
USD ($)
Partnership
Jun. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Partnership
Income Tax Expense [Abstract]          
Number of investments in partnerships | Partnership     4   4
Investment amount in partnerships $ 631,000   $ 631,000   $ 700,000
Investment Tax Credit Carryforward [Member]          
Tax Credit Carryforward [Line Items]          
Investment tax credits 775,000   $ 775,000    
Tax credits recognition period     5 years 6 months    
Tax credits recognized as reduction of tax expense amount 35,000 $ 49,000 $ 70,000 $ 99,000  
Amortization of investment in other expenses $ 40,000 $ 64,000 $ 80,000 $ 129,000