Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Facility Closing [Member]
Pension and other postretirement benefits expenses
Curtailment gain				$ (7,217)
Settlement gain				(230)
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,491	$ 1,572	$ 4,479	4,674
Interest cost	4,336	4,764	13,028	14,051
Expected return on plan assets	(7,615)	(7,206)	(22,392)	(20,882)
Amortization of prior service cost (credit)	141	110	422	330
Amortization of actuarial losses	2,879	2,703	8,719	7,846
Curtailment gain	0	0	0	(7,217)
Settlement gain	0	298	0	(193)
Net periodic benefit cost	1,232	2,241	4,256	(1,391)
Expected company contributions in 2018	4,600		4,600
Pensions [Member] \| Facility Closing [Member]
Pension and other postretirement benefits expenses
Curtailment gain			(7,217)
Settlement gain			(230)	(230)
Pensions [Member] \| Qualified Plan [Member]
Pension and other postretirement benefits expenses
Expected company contributions in 2018	0		0
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	22	20	64	62
Interest cost	338	389	1,019	1,170
Amortization of prior service cost (credit)	5	(17)	15	(51)
Amortization of actuarial losses	135	68	421	207
Net periodic benefit cost	$ 500	$ 460	$ 1,519	$ 1,388

Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan.

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Amount of prior service cost (credit) recognized in net periodic benefit cost (credit) of defined benefit plan.

+ References

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- Definition

Amount of contributions expected to be received by defined benefit plan from employer in fiscal year. Excludes contributions paid by employer in current fiscal year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 6
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2709-114920

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- Definition

Amount of expected return (loss) recognized in net periodic benefit (cost) credit, calculated based on expected long-term rate of return and market-related value of plan assets of defined benefit plan.

+ References

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Amount of cost recognized for passage of time related to defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(2)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Amount of net periodic benefit cost (credit) for defined benefit plan.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from event reducing expected years of future service of present employees or eliminating accrual of defined benefits for some or all future services of present employees.

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Amount of gain (loss) recognized in net periodic benefit (cost) credit from irrevocable action relieving primary responsibility for benefit obligation and eliminating risk related to obligation and assets used to effect settlement.

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- Definition

Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (h)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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