Notes, Mortgage Notes and Obligations Payable - Fourth Quarter 2012 Debt Transaction (Details) (USD $)	12 Months Ended						0 Months Ended		0 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Senior Notes [Member] 8.5% Notes [Member]	Dec. 31, 2011 Senior Notes [Member] 8.5% Notes [Member]	Apr. 26, 2011 Senior Notes [Member] 8.5% Notes [Member]	Oct. 18, 2012 Senior Notes [Member] New 8.5% Notes [Member]	Oct. 18, 2012 Senior Notes [Member] Original 8.5% Notes [Member]	Oct. 18, 2012 Loans Payable [Member] Term Loan Facility [Member]	Oct. 18, 2012 Maximum [Member] Senior Notes [Member] New 8.5% Notes [Member]
Debt Instrument [Line Items]
Debt face amount						$ 500,000,000.0	$ 235,000,000.0	$ 500,000,000.0
Interest rate				8.50%	8.50%	8.50%	8.50%	8.50%
Issuance price, percent of principal amount							107.125%
Period to file registration statement							270 days
Period when registration becomes effective							360 days
Period to complete exchange offer							390 days
Period when shelf registration statement to become effective							480 days
Special interest							0.25%
Special interest, period							90 days
Subsequent increase in special interest							0.25%			1.00%
Subsequent increase in special interest, period							90 days
Net proceeds from the sale of the 8.5% Senior Notes due 2021	251,700,000	500,000,000	0				251,700,000
Initial borrowings under term loan									350,000,000
Payments of accrued interest									1,800,000
Payments of Debt Issuance Costs	5,900,000	59,600,000	9,500,000				4,700,000
Loss from debt retirement	6,400,000	33,800,000	0						6,400,000
Deferred finance costs									3,900,000
Debt premium	$ 5,300,000						$ 15,100,000