Stock-Based Compensation ESPP (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	$ 7.9	$ 7.7	$ 7.1
Shares of Class A common stock available for issuance under ESPP	2,426,852
Stock purchase under ESPP life-to-date	184,180
Compensation expense under ESPP	$ 0.1
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of Class A common stock available for issuance under ESPP	1,265,625