Retirement Plans - Assumptions Used in Accounting for Plans (Detail)	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Discount rate used to calculate benefit obligation	2.40%	2.82%	3.96%
Discount rate used to calculate net periodic pension cost	2.82%	3.96%	3.40%
Executive Compensation
Defined Benefit Plan Disclosure [Line Items]
Average annual increase in compensation	3.25%	3.25%	3.25%
Director Compensation
Defined Benefit Plan Disclosure [Line Items]
Average annual increase in compensation	0.00%	0.00%	0.00%

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

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=118255775&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 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=118255775&loc=d3e1928-114920

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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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