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Summary of Significant Accounting Policies (Details)
12 Months Ended
Dec. 31, 2017
USD ($)
Segment
Dec. 31, 2016
USD ($)
Accounting Policies [Abstract]    
Number of operating segments | Segment 1  
Available-for-sale securities, other than temporary impairment losses $ 0 $ 0
Allowance recorded 0 0
Impaired assets 0 0
Assets held-for-sale $ 0 $ 0