Postretirement Benefits - Actuarial Assumptions (Details)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Actuarial assumptions used to determine benefit obligations:
Discount rate	4.47%	3.73%
Employee pension plan \| Qualified Plan \| Funded Plan
Actuarial assumptions used to determine benefit obligations:
Discount rate			4.24%	4.57%
Compensation increases	3.32%	3.32%	3.32%	3.32%
Actuarial assumptions used to determine net periodic benefit cost:
Discount rate	3.73%	4.24%	4.57%
Expected return on assets	6.75%	6.75%	7.00%	7.00%
Rate of compensation increase	3.32%	3.32%	3.32%
Supplemental employee retirement plan (SERP) \| Nonqualified Plan \| Unfunded plan
Actuarial assumptions used to determine benefit obligations:
Pre-retirement discount rate	4.47%	3.73%	4.24%	4.57%
Post-retirement discount rate	3.97%	3.23%	3.74%	4.07%
Compensation increases	5.00%	5.00%	5.00%	5.00%
Actuarial assumptions used to determine net periodic benefit cost:
Pre-retirement discount rate	3.73%	4.24%	4.57%
Post-retirement discount rate	3.23%	3.74%	4.07%
Rate of compensation increase	5.00%	5.00%	5.00%

The post-retirement interest rate used to adjust for the time value of money for the plan.

No definition available.

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- Definition

The pre-retirement interest rate used to adjust for the time value of money for the plan.

+ References

No definition available.

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- Definition

The post-retirement interest rate used to adjust for the time value of money.

+ References

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- Definition

The pre-retirement interest rate used to adjust for the time value of money.

+ References

No definition available.

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(1)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

+ References

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(2)
-URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920

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