Qualified Employee Benefit Plans - Actuarial Computations Used to Determine Net Periodic Costs (Details) - Retirement Plan	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Assumptions used to determine net periodic benefit costs [Abstract]
Discount rate on benefit obligations	3.35%	4.40%	3.90%
Expected long-term rate of return on plan assets	5.50%	5.75%	5.75%

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.

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)(3)
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2919-114920

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