Retirement Benefits - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses	$ 131,792	$ 130,235	$ 262,265	$ 250,225
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			2,000
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
Accounting Standards Update 2017-17 | Other (Income) Expense Net
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Selling, general and administrative expenses		$ 800		$ 1,600