Pension and Other Postretirement Benefits (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2017	Jun. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Pensions [Member]
Pension and other postretirement benefits expenses
Service cost	$ 1,572		$ 1,354	$ 4,674	$ 4,056
Interest cost	4,764		4,869	14,051	14,650
Expected return on plan assets	(7,206)		(7,564)	(20,882)	(22,774)
Amortization of prior service cost (credit)	110		52	330	157
Amortization of actuarial losses	2,703		2,697	7,846	8,109
Curtailment gain	0		0	(7,217)	0
Settlement loss (gain)	298	$ (230)	0	(193)	0
Net periodic benefit cost	2,241		1,408	(1,391)	4,198
Pensions [Member] \| Domestic Plan [Member] \| Qualified Plan [Member]
Pension and other postretirement benefits expenses
Discretionary contributions				5,000
Pensions [Member] \| Domestic Plan [Member] \| Nonqualified Plan [Member]
Pension and other postretirement benefits expenses
Expected company contributions in 2017	5,000			5,000
Other Postretirement Benefits [Member]
Pension and other postretirement benefits expenses
Service cost	20		31	62	92
Interest cost	389		440	1,170	1,324
Amortization of prior service cost (credit)	(17)		(93)	(51)	(280)
Amortization of actuarial losses	68		134	207	401
Net periodic benefit cost	$ 460		$ 512	$ 1,388	$ 1,537

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)(2)
-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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- References

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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.

+ References

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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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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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