Notes Receivable - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012 SecurityLoan	Dec. 31, 2011 SecurityLoan	Dec. 31, 2010
Mortgage Loans on Real Estate [Line Items]
Number of loans receivable outstanding	6	6
Face value of note receivable sold, including accrued interest		$ 11,800,000
Sale proceeds on note receivable		6,800,000
Past due on interest payments		90 days
Maturity date of the principal amount	September 2011
Principal Amount of Loans subject to delinquent principal or interest	9,800,000
Number of loans outstanding	1
Loan loss reserve	$ 4,300,000	$ 5,000,000	$ 0