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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]      
Unrealized gains (losses) on investments, tax $ 1,814 $ 3,014 $ (1,432)