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Investments - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019	Jan. 01, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Purchase an available-for-sale debt securities with credit deterioration	$ 0			$ 0
Transfer from investments			$ 3,400,000
Carrying value							$ 3,400,000
Note receivable, noncurrent	900,000			900,000		$ 900,000
Asset impairments		$ 3,872,000		65,000	$ 3,872,000
Carrying value of investment	1,800,000			1,800,000
Net Investment Gain (Loss) [Member]
Schedule of Investments [Line Items]
Asset impairments				1,600,000
Other Receivables [Member]
Schedule of Investments [Line Items]
Note receivable, current	4,300,000		$ 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			$ 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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