Interim Financial Statements (Recent Accounting Pronouncements) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Accounting Standards Update 2016-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income tax deficiency from stock-based awards	$ 1.8
Cumulative effect on retained earnings (pre-tax), share-based accounting standard	0.2
Accounting Standards Update 2016-02 [Member] | Minimum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected additional operating lease liability	300.0
Accounting Standards Update 2016-02 [Member] | Maximum [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Expected additional operating lease liability	$ 400.0