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Investments - Additional Information (Detail) - USD ($)	3 Months Ended
Investments - Additional Information (Detail) - USD ($)	Mar. 31, 2020	Mar. 31, 2019	Jan. 01, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Purchase an available-for-sale debt securities with credit deterioration	$ 0
Transfer from investments		$ 3,400,000
Carrying value				$ 3,400,000
Note receivable, noncurrent	900,000		$ 900,000
Asset impairments	65,000
Carrying value of investment	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
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%