Marketable Securities (Narrative) (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2018 USD ($) Number	Dec. 31, 2017 USD ($)
Schedule of Available-for-sale Securities [Line Items]
Available-For-Sale Securities Number of Securities Owned | Number	18
Available-For-Sale Securities Number Of Securities Owned Unrealized Losses | Number	5
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $	$ 5	$ 17
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $	$ 100