Investments in Loans - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 Loan	Jun. 30, 2012	Dec. 31, 2012 Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Commercial real estate loans carrying value		$ 24,871,000		$ 24,871,000
Gains (losses) on assets	224,000	2,518,000	221,000	2,529,000
Number of commercial mortgages			157		150
Average impaired loans unpaid balance	45,979,000	75,728,000	46,450,000	79,811,000
Interest income from impaired loans	2,000	0	21,000	62,000
Outstanding recorded investment in loan before modification			18,995,000
Outstanding recorded investment in loan after modification			18,995,000
Before modification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity date of commercial real estate loans	2014-03		2014-03
After modification
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maturity date of commercial real estate loans	2016-02		2016-02
Series of Individually Immaterial Business Acquisitions
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investments in acquisition of real estate	36,950,000		36,950,000
Gains (losses) on assets			1,550
Series of Individually Immaterial Business Acquisitions | Multi-family real estate properties
Accounts, Notes, Loans and Financing Receivable [Line Items]
Investments in acquisition of real estate	35,400,000		35,400,000
Commercial real estate loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Gains (losses) on assets				2,529,000
Commercial real estate loans on non-accrual status	65,597,000		65,597,000		69,080,000
Weighted-average interest rate	8.20%		8.20%		8.40%
Number of commercial mortgages			15		14
Impaired unpaid principal balances	45,280,000		45,280,000		47,394,000
Other loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average interest rate	7.20%		7.20%
Other loan with carrying amount	$ 14,882,000		$ 14,882,000		$ 18,462,000