Pension and Other Postretirement Benefits - Net Periodic Benefit Cost (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Selling, General and Administrative Expense	$ 276,345	$ 255,612	$ 810,474	$ 760,714
Non-operating Expense	7,828	6,357	22,841	18,503
Pension Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost	7,134	6,604	21,401	19,812
Selling, General and Administrative Expense	7,134	6,604	21,401	19,812
Interest cost	6,830	6,954	20,491	20,863
Expected return on plan assets	(7,966)	(7,658)	(23,897)	(22,973)
Amortization of: Net actuarial loss	6,624	5,376	19,871	16,127
Amortization of: Prior service cost (gain)	79	105	238	315
Non-operating Expense	5,567	4,777	16,703	14,332
Net periodic benefit cost	12,701	11,381	38,104	34,144
Other Postretirement Benefit Plans, Defined Benefit
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Service cost	580	582	1,739	1,745
Selling, General and Administrative Expense	580	582	1,739	1,745
Interest cost	659	711	1,978	2,133
Expected return on plan assets	0	0	0	0
Amortization of: Net actuarial loss	213	197	639	591
Amortization of: Prior service cost (gain)	(489)	(545)	(1,467)	(1,635)
Non-operating Expense	383	363	1,150	1,089
Net periodic benefit cost	$ 963	$ 945	$ 2,889	$ 2,834