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Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Tax Cuts and Jobs Act (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Income Taxes [Line Items]    
Income Tax Benefit, Adjustment of Deferred Tax Assets upon Adoption of TCJA   $ (0.4)
U.S. Internal Revenue Service (IRS) [Member]    
Income Taxes [Line Items]    
Effective income tax rate, percent 21.00% 34.00%