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Investments - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended		12 Months Ended
	Mar. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Schedule of Investments [Line Items]
Available-for-sale debt securities, allowance for credit loss		$ 0	$ 0
Purchase an available-for-sale debt securities with credit deterioration		0
Transfer from investments	$ 3,400,000
Asset impairments			$ 65,000
Carrying value of investment		800,000		$ 800,000
Net Investment Gain (Loss) [Member]
Schedule of Investments [Line Items]
Asset impairments				2,600,000
Other Receivables [Member]
Schedule of Investments [Line Items]
Note receivable, current	$ 4,300,000	4,300,000		4,300,000
Asset impairments		0
Long-term Investments [Member]
Schedule of Investments [Line Items]
Note receivable, noncurrent		$ 900,000		$ 900,000
Investment [Member] | Issuer Concentration [Member] | Market Value of Total Investment Portfolio [Member]
Schedule of Investments [Line Items]
Investment concentration risk percentage		5.00%

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