Pension and Other Postretirement Benefits (Details 1) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Contribution expense		$ 6,644	$ 5,907	$ 5,347
Pension lump-sum settlement charge		0	0	9,856
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension lump-sum settlement charge		21,074	0
Curtailment gain		$ 7,217	$ 0	0
Pension Plan [Member] | Selling, General and Administrative Expenses [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension lump-sum settlement charge				$ 9,856
Retirement Savings Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual retirement contribution percent		4.00%
Facility Closing [Member]
Defined Benefit Plan Disclosure [Line Items]
Curtailment gain	$ 7,217	$ 7,217