Fair Value Measurements (Schedule of Carrying Values and Estimated Fair Values of Debt Instruments) (Details) (USD $)	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 Parent Company [Member]	Dec. 31, 2011 Parent Company [Member]	Dec. 31, 2012 2011 Notes [Member]	Dec. 31, 2011 2011 Notes [Member]	Feb. 14, 2011 2011 Notes [Member]	Dec. 31, 2012 2012 Notes [Member]	Oct. 25, 2012 2012 Notes [Member]	Dec. 31, 2012 Senior Credit Facility [Member]
Debt Instrument [Line Items]
Senior Notes, stated percentage					8.25%			8.25%
Face amount of 8.25% Notes					$ 210,000,000		$ 210.0	$ 300.0	$ 300.0
Carrying Value	689,911,000	204,390,000	689,911,000	204,390,000	205,125,000	204,390,000		289,786,000		195,000,000
Estimated fair value	$ 719,600,000	$ 202,700,000			$ 214,700,000	$ 202,700,000		$ 309,900,000		$ 195,000,000