Fair Value Measurements Cash Flow Model Critical Assumptions (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Increase in Investments in Unconsolidated LLCs and other joint agreements	$ 22.4
Limited Partners' Contributed Capital	34.1
Notes Receivable, Related Parties	2.5
Capitalized Interest and Other Costs Included in Investment in Unconsolidated LLCs and other joint agreements	$ 0.7	$ 0.8
Minimum [Member]
Equity Method Investment, Ownership Percentage	25.00%
Discount Rate Used in Determining Fair Value of Investments in Unconsolidated LLCs and other joint agreements	13.00%
Maximum [Member]
Equity Method Investment, Ownership Percentage	61.00%
Discount Rate Used in Determining Fair Value of Investments in Unconsolidated LLCs and other joint agreements	16.00%
2013 [Member]
Weighted Average Sales Price Increase	0.00%
Weighted Average Increase of Assumed Costs	0.00%
2014 and 2015 [Member]
Weighted Average Sales Price Increase	4.00%
Weighted Average Increase of Assumed Costs	4.00%
2016 and Beyond [Member]
Weighted Average Sales Price Increase	2.00%
Weighted Average Increase of Assumed Costs	2.00%