Stock-Based Compensation ESPP (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares of Class A common stock available for issuance under ESPP	2,174,314
Total stock issued under ESPP since inception	197,375
Compensation expense under ESPP	$ 0.1	$ 0.1	$ 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