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Fair Value Measurement - Additional Information (Detail) - USD ($)
$ in Thousands
9 Months Ended 12 Months Ended
Sep. 30, 2020
Dec. 31, 2019
Fair Value Measurement [Line Items]    
Carrying value of debt $ 235,968 $ 281,625
Restricted investments 21,500 22,600
Fixed-rate Borrowings [Member]    
Fair Value Measurement [Line Items]    
Increase (decrease) in fair value of debt 7,300 3,800
Carrying value of debt $ 236,000 $ 281,600