XML 41 R30.htm IDEA: XBRL DOCUMENT v3.7.0.1
Long-Term Investments - Rollforward of Credit (Gain) Loss Recognized in Earnings on Failed Auction Security (Detail) - Failed Auction Security [Member] - USD ($)
6 Months Ended
Jun. 30, 2017
Jun. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]    
Balance at the beginning of the period $ 59,000 $ 72,000
Reductions in the amount related to credit gain for which other-than-temporary impairment was not previously recognized (6,000) (7,000)
Balance at the end of the period $ 53,000 $ 65,000