Summary of Significant Accounting Policies Summary of Significant Accounting Policies - Recently Adopted Accounting Standards (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	$ (10.9)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reclassification of the stranded tax effects related to the Tax Act (Note 10)	$ 10.9