Cash Equivalents and Investments (Narrative) (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Cash Equivalents and Investments [Abstract]
Gross realized gains (losses)	$ 0	$ 0

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