Financial Instruments (Narrative) (Details) (USD $)	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010
Financial Instruments [Abstract]
Carrying amounts of cash and cash equivalents	$ 480,600,000	$ 298,600,000	$ 480,600,000	$ 376,900,000	$ 315,800,000
Restricted cash		$ 0	$ 1,500,000