Fair Value Measurements - Carrying Value and Estimated Fair Value of Financial Instruments Not Recorded at Fair Value on a Recurring Basis (Detail) (USD $)	Sep. 30, 2013	Dec. 31, 2012	Aug. 31, 2012
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Loans receivable	$ 108,163,000	$ 211,250,000
Secured financing receivable	30,395,000
Mortgage loans payable	308,049,000	280,576,000
Senior notes payable	86,250,000	86,250,000	86,250,000
Secured financings	29,150,000	52,920,000
Notes payable	1,664,000	1,676,000
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Loans receivable
Mortgage loans payable
Senior notes payable	89,666,000	89,183,000
Secured financings
Notes payable
Significant Other Observable Inputs (Level 2) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Loans receivable
Mortgage loans payable
Senior notes payable
Secured financings
Notes payable
Significant Unobservable Inputs (Level 3) [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Loans receivable	122,876,000	222,246,000
Secured financing receivable	30,395,000
Mortgage loans payable	296,678,000	270,923,000
Senior notes payable
Secured financings	29,366,000	53,253,000
Notes payable	1,664,000	1,676,000
Fair Value [Member]
Fair Value Of Assets And Liabilities Measured On Non Recurring Basis [Line Items]
Loans receivable	122,876,000	222,246,000
Secured financing receivable	30,395,000
Mortgage loans payable	296,678,000	270,923,000
Senior notes payable	89,666,000	89,183,000
Secured financings	29,366,000	53,253,000
Notes payable	$ 1,664,000	$ 1,676,000