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Pension and Other Postretirement Benefit Plans - Summary of Change in Plan Assets Valued Using Significant Unobservable Inputs (Level 3) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Level 3    
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]    
Fair value of assets, beginning balance $ 9,948  
Fair value of assets, ending balance 8,735 $ 9,948
Real Estate    
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]    
Fair value of assets, beginning balance 9,948  
Contributions 87 331
Net distributions (300) (11,235)
Redemptions (573)  
Advisory fee (92) (205)
Net investment income 400 771
Unrealized gain (728) (541)
Net realized gain (7) (9)
Fair value of assets, ending balance 8,735 9,948
Real Estate | Level 3    
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]    
Fair value of assets, beginning balance 9,948 20,836
Fair value of assets, ending balance $ 8,735 $ 9,948