Retirement Plans - Weighted Average Assumptions Used to Determine Benefit Obligations (Detail)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	0.00%	0.00%	0.00%
Long-term rate of return on plan assets	7.00%	7.00%
Benefit Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate on benefit obligation	3.51%	4.00%	4.16%
Long-term rate of return on plan assets	7.00%	7.00%	7.00%
Rate of compensation increase	0.00%	0.00%	0.00%
Net Periodic Pension Cost [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate on benefit obligation	4.00%	4.16%	3.69%
Long-term rate of return on plan assets	7.00%	7.00%	7.00%
Rate of compensation increase	0.00%	0.00%	0.00%

Defined Benefit Plan Assumptions Used Calculating Benefit Obligation Expected Long Term Return On Assets

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

+ Details

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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://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

+ Details

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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://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

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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