Long-Term Investments - Additional Information (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019	Dec. 31, 2018
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Minimum period for which failed auction securities been in unrealized loss position	12 months
Aggregate credit loss			$ 39,000	$ 41,000
Failed Auction Security [Member]
Unrealized Losses On Short Term And Long Term Investments [Line Items]
Amortized cost of securities	$ 3,000,000	$ 3,000,000
Period for which failed auction securities been in unrealized loss position	exceeds 12 months
Estimated Fair Value	$ 2,555,000	2,510,000
Gross Unrealized Losses	445,000	490,000
Aggregate credit loss	35,000	$ 37,000
Aggregate temporary impairment loss	$ 410,000