Schedule IV-Mortgage Loans on Real Estate (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Mortgage loans on real estate
Face Amount of Mortgages	$ 1,898,888,000
Carrying Amount of Mortgages	1,421,654,000	2,449,554,000	4,012,067,000	6,662,379,000
Asset specific reserves on impaired loans	482,300,000
Principal amount of loan in default that is more than 90 days delinquent	90 days
Senior Mortgages [Member]
Mortgage loans on real estate
Face Amount of Mortgages	1,746,877,000
Carrying Amount of Mortgages	1,308,495,000
Borrower A
Mortgage loans on real estate
Face Amount of Mortgages	99,725,000
Carrying Amount of Mortgages	99,730,000
Borrower A | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.30%
Variable rate basis	LIBOR
Borrower A | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.30%
Variable rate basis	LIBOR
Borrower B
Mortgage loans on real estate
Face Amount of Mortgages	96,997,000
Carrying Amount of Mortgages	98,055,000
Borrower B | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Variable rate basis	LIBOR
Borrower B | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Variable rate basis	LIBOR
Borrower C(3)
Mortgage loans on real estate
Face Amount of Mortgages	221,358,000
Carrying Amount of Mortgages	74,541,000
Delinquency period for a loan to be considered as non-performing and on non-accrual status	221,400,000
Borrower C(3) | Contractual Interest Accrual Rates
Mortgage loans on real estate
Fixed interest rate (as a percent)	17.00%
Borrower C(3) | Contractual Interest Payment Rates
Mortgage loans on real estate
Fixed interest rate (as a percent)	17.00%
Borrower D(4)
Mortgage loans on real estate
Face Amount of Mortgages	71,480,000
Carrying Amount of Mortgages	62,248,000
Borrower D(4) | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Borrower D(4) | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Variable rate basis	LIBOR
Borrower D(4) | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Variable rate basis	LIBOR
Borrower E(5)
Mortgage loans on real estate
Face Amount of Mortgages	59,338,000
Carrying Amount of Mortgages	59,474,000
Borrower E(5) | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	4.00%
Borrower E(5) | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	4.00%
Variable rate basis	LIBOR
Borrower E(5) | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	4.00%
Variable rate basis	LIBOR
Borrower F(6)
Mortgage loans on real estate
Face Amount of Mortgages	137,807,000
Carrying Amount of Mortgages	56,087,000
Delinquency period for a loan to be considered as non-performing and on non-accrual status	137,800,000
Borrower F(6) | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.50%
Variable rate basis	LIBOR
Borrower F(6) | Contractual Interest Payment Rates
Mortgage loans on real estate
Fixed interest rate (as a percent)	0.00%
Borrower G(7)
Mortgage loans on real estate
Face Amount of Mortgages	55,830,000
Carrying Amount of Mortgages	55,816,000
Borrower G(7) | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	4.25%
Variable rate basis	LIBOR
Borrower G(7) | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	4.25%
Variable rate basis	LIBOR
Borrower H
Mortgage loans on real estate
Face Amount of Mortgages	54,596,000
Carrying Amount of Mortgages	51,705,000
Borrower H | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.88%
Borrower H | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	1.50%
Variable rate basis	LIBOR
Borrower H | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	1.50%
Variable rate basis	LIBOR
Borrower I
Mortgage loans on real estate
Face Amount of Mortgages	46,910,000
Carrying Amount of Mortgages	47,666,000
Borrower I | Contractual Interest Accrual Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	7.00%
Variable rate basis	LIBOR
Borrower I | Contractual Interest Payment Rates
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	7.00%
Variable rate basis	LIBOR
Senior mortgages individually 3%
Mortgage loans on real estate
Face Amount of Mortgages	902,836,000
Carrying Amount of Mortgages	703,173,000
Senior mortgages individually 3% | Contractual Interest Accrual Rates
Mortgage loans on real estate
Fixed interest rate, low end of range (as a percent)	4.00%
Fixed interest rate, high end of range (as a percent)	23.00%
Senior mortgages individually 3% | Contractual Interest Accrual Rates | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	1.50%
Variable rate basis	LIBOR
Senior mortgages individually 3% | Contractual Interest Accrual Rates | Maximum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	8.25%
Variable rate basis	LIBOR
Senior mortgages individually 3% | Contractual Interest Payment Rates
Mortgage loans on real estate
Fixed interest rate, low end of range (as a percent)	2.50%
Fixed interest rate, high end of range (as a percent)	10.00%
Senior mortgages individually 3% | Contractual Interest Payment Rates | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	0.50%
Variable rate basis	LIBOR
Senior mortgages individually 3% | Contractual Interest Payment Rates | Maximum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	8.25%
Variable rate basis	LIBOR
Subordinate Mortgages
Mortgage loans on real estate
Face Amount of Mortgages	152,011,000
Carrying Amount of Mortgages	113,159,000
Subordinate mortgages individually 3%
Mortgage loans on real estate
Face Amount of Mortgages	152,011,000
Carrying Amount of Mortgages	$ 113,159,000
Subordinate mortgages individually 3% | Contractual Interest Accrual Rates
Mortgage loans on real estate
Fixed interest rate, low end of range (as a percent)	5.00%
Fixed interest rate, high end of range (as a percent)	14.00%
Subordinate mortgages individually 3% | Contractual Interest Accrual Rates | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.98%
Variable rate basis	LIBOR
Subordinate mortgages individually 3% | Contractual Interest Accrual Rates | Maximum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.98%
Variable rate basis	LIBOR
Subordinate mortgages individually 3% | Contractual Interest Payment Rates
Mortgage loans on real estate
Fixed interest rate, low end of range (as a percent)	6.50%
Fixed interest rate, high end of range (as a percent)	10.50%
Subordinate mortgages individually 3% | Contractual Interest Payment Rates | Minimum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.98%
Variable rate basis	LIBOR
Subordinate mortgages individually 3% | Contractual Interest Payment Rates | Maximum
Mortgage loans on real estate
Basis spread on variable rate (as a percent)	3.98%
Variable rate basis	LIBOR