Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2016
Income Taxes [Line Items]
U.S. federal statutory rate			35.00%
Effective income tax rate	22.10%	25.80%	23.70%	28.70%
Income before income taxes, domestic operations			$ 13.7	$ 57.2
Income before income taxes, foreign operations			103.7	96.0
Liabilities for uncertain income tax positions	$ 48.7		48.7							$ 46.5
Cash paid for income taxes			46.6	$ 40.4
Prepaid tax payments	$ 9.2		$ 9.2							$ 0.0
Massachusetts Department of revenue [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination					2015	2014
California Franchise Tax Board [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination							2013	2012
Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination						2014	2013	2012
New York State Division of Taxation and Finance [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination						2014	2013	2012	2011
EVDY [Member] | Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Income Tax Examination, Year under Examination						2014