Subsequent Events (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		12 Months Ended		0 Months Ended
	Jun. 30, 2012	Nov. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Jan. 22, 2013 Subsequent Event [Member]	Dec. 31, 2012 2008 Notes [Member]	Jun. 25, 2012 2008 Notes [Member]	Feb. 15, 2013 2008 Notes [Member] Subsequent Event [Member]
Subsequent Event [Line Items]
Return of borrowed shares (in shares)	659,340	701,102	659,340	701,102	2,439,558
Notes repurchased						$ 50.3	$ 15.0	$ 5.2