Financial Instruments (Narrative) (Details) (Auction Rate Securities [Member])	3 Months Ended
	Mar. 31, 2013 item
Schedule of Available-for-sale Securities [Line Items]
Number Of Securities	2
Redemption of available for sale securities, percentage	100.00%
Minimum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	19 years
Maximum [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment maturity period	29 years