Long-Term Investments - Rollforward of Credit (Gain) Loss Recognized in Earnings on Available-for-Sale Auction Rate Securities (Detail) - Failed Auction Security [Member] - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]
Balance at the beginning of the period	$ 41,000	$ 48,000	$ 59,000
Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized	(4,000)	(7,000)	(11,000)
Balance at the end of the period	$ 37,000	$ 41,000	$ 48,000