XML 42 R32.htm IDEA: XBRL DOCUMENT v3.10.0.1
Short-Term Investments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Investments Debt And Equity Securities [Abstract]        
Realized gains (losses) on short-term investments $ 0 $ 0 $ 0 $ 0
Other-than-temporary impairments recognized $ 0 $ 0 $ 0 $ 0