Stock-Based Compensation Stock-Based Compensation - Cash Required to Settle Payments on Restricted Stock Units (Details) (Restricted stock units and stock grants, USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
2008 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	$ 0	$ 0	$ 1.9
2009 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	0	3.0	1.7
2010 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	2.3	2.3	0.6
2011 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	2.4	2.5	0.7
2012 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	2.1	2.2	0
2013 Grant
Stock-Based Compensation
Cash required to settle the payment for grant	$ 2.1	$ 0	$ 0