Fair Value Measurement (Narrative) (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Auction rate security bond par value	$ 1,000,000	$ 1,000,000
Percentage of auction rate security guaranteed	97.00%	97.00%
Minimum [Member]
Percentage of carrying value of auction rate securities	3.00%	3.00%
Maximum [Member]
Percentage of carrying value of auction rate securities	4.00%	4.00%