Summary of Significant Accounting Policies Stock-based Compensation (Details 2) $ in Millions |
12 Months Ended |
---|---|
Dec. 31, 2017
USD ($)
| |
Stock-Based Compensation [Abstract] | |
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $ 18.6 |
Employee Service Share-based Compensation, Outstanding, Weighted Average Remaining Vesting Period | 1 year 4 months |