Financial Instruments - Additional Information (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Investments Debt And Equity Securities [Abstract]
Available for sale securities, continuous loss position, 12 months or longer	$ 0	$ 0

This item represents the aggregate fair value of investments in debt and equity securities categorized neither as held-to-maturity nor trading securities that have been in a continuous unrealized loss position for twelve months or longer.

No definition available.

Name:	us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant