Marketable Securities (Narrative) (Details)	3 Months Ended
Mar. 31, 2012 M
Marketable Securities [Abstract]
Remaining maturities of marketable debt securities, start date	May 2012
Remaining maturities of marketable debt securities, end date	December 2014
Weighted-average remaining maturity period of marketable debt securities, months	15

The earliest date, in a range of maturity dates, that a debt security categorized as neither trading nor held-to-maturity is scheduled to be repaid.

No definition available.

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Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration