Debt and Preferred Equity Investments (Details 4) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Dec. 31, 2012 item
Debt and Preferred Equity Investments
Financing receivables past due 90 days	$ 0
Nonaccrual balance of financing receivables	0
Number of portfolio segments of financial receivables	1		1
Additional amount of financing receivables	129,000,000		121,300,000
Unpaid Principal Balance
Unpaid Principal Balance	10,750,000		10,750,000
Recorded Investment
Recorded Investment	10,750,000		10,750,000
Allowance Allocated
Allowance Allocated	7,000,000		7,000,000
Average recorded investment in impaired loans	10,864,000	79,937,000
Investment and preferred equity income (loss) recognized	227,000	1,562,000
Commercial real estate
Unpaid Principal Balance
With an allowance recorded	10,750,000		10,750,000
Recorded Investment
With an allowance recorded	10,750,000		10,750,000
Allowance Allocated
Allowance Allocated	$ 7,000,000		$ 7,000,000