Mortgage Loans on Real Estate (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Principal Amount of Loans subject to delinquent principal or interest	$ 9,800
Balance at beginning of period	84,541	103,705	58,719	60,378
Additions during period:
New mortgage loans	160,995	10,000	60,618
Interest	4,949	811	3,106
Accretion of discount	826	780	250
Deductions during period:
Provision for loan loss reserve	(4,300)	(5,000)	0
Collections of principal	(104)	(25,755)	0
Foreclosures	0	0	(18,988)
Balance at close of period	246,907	84,541	103,705
INVESTMENTS IN AND ADVANCES TO JOINT VENTURES [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens	1,243,254			1,243,254
Face Amount of Mortgages	332,266			332,266
Carrying Amount of Mortgages	246,907			246,907
Principal Amount of Loans subject to delinquent principal or interest	86,995			86,995
SENIOR LOANS and MEZZANINE LOANS Multi-family [Member]
Mortgage Loans on Real Estate [Line Items]
Prior Liens	153,240			153,240
Face Amount of Mortgages	82,964			82,964
Carrying Amount of Mortgages	60,378			60,378
Principal Amount of Loans subject to delinquent principal or interest	20,149			20,149
Borrower A [Member] | SENIOR LOANS [Member] | Retail [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	5.73%
Final Maturity Date	Sep-17
Periodic Payment Terms	Interest and principal
Prior Liens	0
Face Amount of Mortgages	33,000
Carrying Amount of Mortgages	28,509
Principal Amount of Loans subject to delinquent principal or interest	0
Borrower B [Member] | MEZZANINE LOANS Multi-family [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	LIBOR+6.0%, Floor 11%
Final Maturity Date	Feb-17
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	26,000
Face Amount of Mortgages	5,868
Carrying Amount of Mortgages	5,923
Principal Amount of Loans subject to delinquent principal or interest	0
Borrower C [Member] | Retail [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	11.00%
Final Maturity Date	Jun-13
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	51,750
Face Amount of Mortgages	12,800
Carrying Amount of Mortgages	11,342
Principal Amount of Loans subject to delinquent principal or interest	0
Borrower D [Member] | Retail [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	10.00%
Final Maturity Date	Nov-22
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	59,000
Face Amount of Mortgages	9,000
Carrying Amount of Mortgages	9,078
Principal Amount of Loans subject to delinquent principal or interest	0
Borrower E [Member] | Mixed Use [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	LIBOR+10.0%, Floor 14%
Final Maturity Date	on demand (loan in default)
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	2,500
Face Amount of Mortgages	11,490
Carrying Amount of Mortgages	5,526
Principal Amount of Loans subject to delinquent principal or interest	9,343
Borrower F [Member] | Mixed Use [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	LIBOR+8.0%, Floor 12%
Final Maturity Date	on demand (loan in default)
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	13,990
Face Amount of Mortgages	10,806
Carrying Amount of Mortgages	0
Principal Amount of Loans subject to delinquent principal or interest	10,806
Borrower G [Member] | INVESTMENTS IN AND ADVANCES TO JOINT VENTURES [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	LIBOR+7.0%, Floor 12%
Final Maturity Date	on demand (loan in default)
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	0
Face Amount of Mortgages	66,846
Carrying Amount of Mortgages	0
Principal Amount of Loans subject to delinquent principal or interest	66,846
Borrower H [Member] | INVESTMENTS IN AND ADVANCES TO JOINT VENTURES [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	10.00%
Final Maturity Date	Oct-17
Periodic Payment Terms	Interest monthly, principal at maturity
Prior Liens	137,869
Face Amount of Mortgages	31,700
Carrying Amount of Mortgages	31,973
Principal Amount of Loans subject to delinquent principal or interest	0
Borrower I [Member] | INVESTMENTS IN AND ADVANCES TO JOINT VENTURES [Member]
Mortgage Loans on Real Estate [Line Items]
Interest Rate	10.00%
Final Maturity Date	Jun-19
Periodic Payment Terms	Interest quarterly (partial payment), principal and unpaid interest at maturity
Prior Liens	952,145
Face Amount of Mortgages	150,756
Carrying Amount of Mortgages	154,556
Principal Amount of Loans subject to delinquent principal or interest	$ 0