Fair Value Measurement (Narrative) (Details) (USD $)	6 Months Ended	12 Months Ended	18 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Minimum [Member]	Jun. 30, 2012 Maximum [Member]
Auction rate security bond par value	$ 4,000,000	$ 5,000,000
Percentage of auction rate security guaranteed	75.20%	79.60%
Percentage of carrying value of auction rate securities			3.00%	4.00%