Summary of Significant Accounting Policies Recent Accounting Pronouncement ASU 2016-09 (Details) $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($)
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ 3.4
Change in Forfeiture Policy
Cumulative Effect of New Accounting Principle in Period of Adoption	0.4
Unrecognized Excess Tax Benefit
Cumulative Effect of New Accounting Principle in Period of Adoption	$ 1.0