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Marketable Securities (Narrative) (Details)	3 Months Ended
Marketable Securities (Narrative) (Details)	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Government And Agency Securities [Member] Level 1 [Member] M	Dec. 31, 2011 Government And Agency Securities [Member] Level 1 [Member] M	Mar. 31, 2011 Government And Agency Securities [Member] Level 1 [Member] M
Schedule of Trading Securities and Other Trading Assets [Line Items]
Transfers between levels during the period	0	0
Debt instrument maturity date in months			12	12	12