Marketable Securities (Narrative) (Details) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010
Dollar value of transfers between levels	$ 0	$ 0
Government And Agency Securities [Member] | Level 1 - Quoted Prices In Active Markets For Identical Assets [Member]
Debt instrument maturity date in months	12