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Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Obligation (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Weighted Average Assumptions Used to Determine Benefit Obligation
First five years	1.96%	1.47%
Five years to twenty years	3.58%	3.34%
After twenty years	4.35%	4.30%
Expected return on plan assets	1.00%	7.50%
Rate of compensation increase		3.00%

X

- Definition

Defined benefit plan assumptions used calculating benefit obligation discount rate after twenty years.

+ References

No definition available.

+ Details

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X

- Definition

Defined benefit plan assumptions used calculating benefit obligation discount rate first five years.

+ References

No definition available.

+ Details

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X

- Definition

Defined benefit plan assumptions used calculating benefit obligation discount rate five year to twenty years.

+ References

No definition available.

+ Details

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X

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

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X

- 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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (k)(3)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- References

No definition available.

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