Retirement Benefits - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses	$ (131,426)	$ (119,114)	$ (393,691)	$ (369,339)
Other (income) expense - net	(1,653)	1,513	(1,717)	2,496
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			4,200
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contribution for next fiscal year					$ 5,800
Expected contributions in current fiscal year	4,800		4,800
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Expected contribution for next fiscal year					$ 100
Expected contributions in current fiscal year	600		600
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-17
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses		$ 800		$ 2,400
Other (income) expense - net	$ 900		$ 2,500