Significant Accounting Policies (Details 4) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Significant Accounting Policies
Days past due for income recognition on debt and preferred equity investments to be suspended	90 days
Reserve for Possible Credit Losses
Loan loss reserves and charge offs		$ 564,000
Loan loss reserves or charge-offs on investments being held to maturity	0	3,000,000	3,000,000
Recoveries recorded		2,400,000	2,436,000
Income taxes
Minimum annual taxable income distributed to stockholders to maintain REIT qualification (as a percent)	90.00%
Federal, state and local tax provision	1,600,000	0
Estimated tax payments	100,000	0
Debt and Preferred Equity Investments Held to Maturity
Reserve for Possible Credit Losses
Loan loss reserves and charge offs	$ 0