Financial Statement Presentation - Narrative (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Jan. 01, 2017
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect adjustment					$ 42.2
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-07
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other (income) expense	$ 2.6	$ 1.2	$ 1.6	$ 1.4