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Employee Benefit Plans - Summary of Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Detail) - Supplemental Employee Retirement Plan [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Weighted-average assumptions used to determine Net Periodic Benefit Cost
Discount rate	2.95%	4.00%
Corridor	10.00%	10.00%
Average future working lifetime	6 years 5 months 23 days	6 years 5 months 15 days
Mortality table	Pri-2012	RP-2014
Mortality improvement scale	MP-2019	MP-2018

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- Definition

Defined benefit plan assumptions used calculating net periodic benefit cost corridor.

+ References

No definition available.

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- Definition

Defined benefit plan weighted average assumptions for determining periodic net benefits costs average future working life time.

+ References

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- Definition

Defined benefit plan weighted average assumptions for determining periodic net benefits costs description of mortality.

+ References

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- Definition

Defined benefit plan weighted average assumptions for determining periodic net benefits costs description of mortality improvement scale.

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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-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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