XML 64 R31.htm IDEA: XBRL DOCUMENT v3.20.1
Long-Term Investments - Rollforward of Credit (Gain) Loss Recognized in Earnings on Available-for-Sale Auction Rate Securities (Detail) - USD ($)
 3 Months Ended
Mar. 31, 2020
Mar. 31, 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   (1,000)
Balance at the end of the period   $ 40,000
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 (1,000)  
Balance at the end of the period $ 36,000