Retirement Plans - Expected Benefit Payments to Participants and Estimated Contributions to be Made by Company (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Retirement Benefits [Abstract]
Expected Benefit Payments to Participants, 2018	$ 1,106
Expected Benefit Payments to Participants, 2019	1,067
Expected Benefit Payments to Participants, 2020	1,233
Expected Benefit Payments to Participants, 2021	1,859
Expected Benefit Payments to Participants, 2022	2,008
Expected Benefit Payments to Participants, 2023-2027	10,169
Estimated Company Contributions, 2018	1,106
Estimated Company Contributions, 2019	1,067
Estimated Company Contributions, 2020	1,233
Estimated Company Contributions, 2021	1,859
Estimated Company Contributions, 2022	2,008
Estimated Company Contributions, 2023-2027	$ 10,169

Defined benefit plan estimated future employer contributions five fiscal years thereafter.

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- Definition

Defined benefit plan estimated future employer contributions in year five.

+ References

No definition available.

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- Definition

Defined benefit plan estimated future employer contributions in year four.

+ References

No definition available.

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- Definition

Defined benefit plan estimated future employer contributions in year three.

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No definition available.

+ Details

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- Definition

Defined benefit plan estimated future employer contributions in year two.

+ References

No definition available.

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- Definition

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

+ 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 (f)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References

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- Definition

Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

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- Definition

Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

+ References

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- Definition

Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

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- Definition

Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

+ References

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- Definition

Amount of contributions expected to be received by defined benefit plan from employer in next fiscal year following latest fiscal year.

+ 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 (g)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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