Summary of Significant Accounting Policies (Cost of Sales and Selling, General and Administrative Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Distribution | General and administrative expenses
Component of Operating Other Cost and Expense [Line Items]
Inventory related costs, including purchasing costs, receiving costs and inspection costs	$ 3.5	$ 3.5	$ 3.2