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Summary of Significant Accounting Policies Stock-based Compensation (Details 2)
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
Accounting Policies [Abstract]  
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized $ 22.3
Employee Service Share-based Compensation, Outstanding, Weighted Average Remaining Vesting Period 1 year 2 months