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Fair Value Measurement - Additional Information (Detail) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Fair Value Measurement [Line Items]    
Carrying value of debt $ 258,250 $ 270,359
Restricted investments 23,100 23,400
Fixed-rate Borrowings [Member]    
Fair Value Measurement [Line Items]    
Increase (decrease) in fair value of debt 2,000 6,100
Carrying value of debt $ 258,200 $ 270,400