Long-Term Investments - Rollforward of Credit (Gain) Loss Recognized in Earnings on Available-for-Sale Auction Rate Securities (Detail) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance at the beginning of the period		$ 41,000
Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized		(2,000)
Balance at the end of the period		$ 39,000
Failed Auction Security [Member]
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance at the beginning of the period	$ 37,000
Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized	(2,000)
Balance at the end of the period	$ 35,000