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Summary of Significant Accounting Policies Cash and Cash Equivalents (Details)
Dec. 31, 2018
USD ($)
Bank
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Accounting Policies [Abstract]        
Number of Banks in Which Cash is Held | Bank 1      
Cash and cash equivalents | $ $ 1,891,000 $ 26,780,000 $ 28,285,000 $ 8,943,000