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Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Statement Of Income And Comprehensive Income [Abstract]      
Net actuarial loss arising in period, tax benefit (expense) $ 265 $ (1,263) $ 2,300
Amortization of prior service cost included in pension expense, tax 3 3 3
Amortization of actuarial loss included in pension expense, tax $ 1,089 $ 657 $ 979