Financial Instruments - Additional Information (Detail)	9 Months Ended
Sep. 30, 2019 USD ($)
Financial Instrument [Line Items]
Material realized gains or losses on available-for-sale securities	$ 0
Maximum
Financial Instrument [Line Items]
Available for sale debt securities contractual maturities	1 year

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

No definition available.

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