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Retirement Plans (Plan's Allocated Target and Ranges and Actual Weighted Average Asset Allocation by Investment Categories) (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Actual percentage	100.00%	100.00%
Range minimum	0.00%
Range maximum	0.00%
Maximum percentage of equity security value of total plans portfolio value that is allowed	8.00%
Maximum percentage of any corporation outstanding shares that is allowed for retirement income plan equity portfolio	5.00%
Extended Duration Fixed Maturity [Member]
Actual percentage	53.00%	60.00%
Range minimum	40.00%
Range maximum	100.00%
Global Equity [Member]
Actual percentage	33.00%	36.00%
Range minimum	0.00%
Range maximum	40.00%
Private Equity Funds [Member]
Actual percentage	6.00%	3.00%
Range minimum	0.00%
Range maximum	30.00%
Cash And Short Term Investments [Member]
Actual percentage	8.00%	1.00%
Range minimum	0.00%
Range maximum	5.00%

X

- Definition

The maximum percentage of outstanding shares of any one corporation that is allowed for the Retirement Income Plan.

+ References

No definition available.

+ Details

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X

- Definition

The maximum percentage of any individual security value of the total Retirement Income Plan's portfolio value that is allowed.

+ References

No definition available.

+ Details

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X

- Definition

Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

+ Details

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Period Type:	duration

X

- Definition

Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ 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 (d)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&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 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

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X

- Definition

Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

+ Details

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X

- Details

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X

- Details

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X

- Details

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- Details

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