Related Party Transactions - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012	Jun. 30, 2013		Jun. 30, 2012	Dec. 31, 2012
Related Party Transaction [Line Items]
Percentage of outstanding Wraparound mortgages payable owned by NPAEP	100.00%			100.00%
Accounts payable and other liabilities	$ 3,464	[1]		$ 3,464	[1]		$ 3,576	[1]
Maximum borrowing capacity	2,500			2,500
Variable rate of interest on prime rate	3.25%			3.25%
Line of credit facility, expiration date				December 2013
Line of credit facility, amount outstanding	1,069			1,069
Interest payable	163			163
Annual rental payments to NPAEP	8		8	17		13
Accounts Payable And Other Liabilities
Related Party Transaction [Line Items]
Accounts payable and other liabilities	$ 2,888			$ 2,888			$ 2,836

[1] See Note 3: Related Party Transactions.