Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2019	Sep. 30, 2019
Marketable Securities [Abstract]
Realized gains or losses on marketable securities	$ 0	$ 0

Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

No definition available.

Name:	us-gaap_MarketableSecuritiesRealizedGainLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration