Employee Benefit Plans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Change in benefit obligation
Benefit obligation at beginning of year	$ 7,112	$ 8,677
Service cost	0	0	$ 236
Interest cost	155	194	182
Actuarial (gains) losses	(245)	(421)
Participant contributions	0	0
Retiree drug subsidy received	0	0
Benefits paid	(1,190)	(1,338)
Benefit obligation at end of year	5,832	7,112	8,677
Change in plan assets
Fair value of plan assets at beginning of year	0	285
Actual gains on plan assets	0	0
Company contributions	1,190	1,053
Participant contributions	0	0
Benefits paid	(1,190)	(1,338)
Fair value of plan assets at end of year	0	0	285
Under funded status of plans at end of year	(5,832)	(7,112)
Postretirement Benefits
Change in benefit obligation
Benefit obligation at beginning of year	29,757	39,152
Service cost	391	760	900
Interest cost	985	1,549	1,584
Actuarial (gains) losses	(7,903)	(10,823)
Participant contributions	463	653
Retiree drug subsidy received	184	5
Benefits paid	(1,275)	(1,539)
Benefit obligation at end of year	22,602	29,757	39,152
Change in plan assets
Fair value of plan assets at beginning of year	0	0
Actual gains on plan assets	0	0
Company contributions	812	886
Participant contributions	463	653
Benefits paid	(1,275)	(1,539)
Fair value of plan assets at end of year	0	0	$ 0
Under funded status of plans at end of year	$ (22,602)	$ (29,757)

Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses.

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- Definition

Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan.

+ References

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- Definition

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

+ References

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Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 60
-Section 50
-Paragraph 4
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- Definition

Amount of contributions received by defined benefit plan from participant which increase benefit obligation.

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- Definition

Amount, before benefit payment, of receipt from prescription drug subsidy which increases benefit obligation of defined benefit postretirement plan.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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- Definition

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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-SubTopic 20
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- Definition

Fair value of assets that have been segregated and restricted to provide pension or postretirement benefits. Assets include, but are not limited to, stocks, bonds, other investments, earnings from investments, and contributions by the employer and employees.

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- Definition

Amount of funded (unfunded) status of defined benefit plan, measured as difference between fair value of plan assets and benefit obligation. Includes, but is not limited to, overfunded (underfunded) status.

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- Definition

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

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- Definition

Amount of payment to participant under defined benefit plan which decreases plan assets. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 60
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-URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964

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- Definition

Amount of contributions received by defined benefit plan from participant which increases plan assets.

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- Definition

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

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- Details

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