Indebtedness - Summary of Indebtedness at Estimated Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	$ 599,985		$ 677,890
Senior Unsecured Debt, Net, Carrying Amount	364,861		445,916
Unsecured Term Loan, Carrying Amount	200,000		0
Unsecured Credit Facility, Carrying Amount	185,000		173,000
Total, Carrying Amount	1,349,846		1,296,806
Total, Fair Value	1,422,460		1,340,695
Mortgages
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	599,985		677,890
Mortgage Loans Payable, Net, Fair Value	640,818		684,914
Senior Unsecured Notes
Debt Disclosure [Line Items]
Senior Unsecured Debt, Net, Carrying Amount	364,861		445,916
Senior Unsecured Debt, Net, Fair Value	395,320		482,781
Unsecured Term Loan
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount	200,000	[1]
Unsecured Term Loan, Fair Value	200,575
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	185,000	[2]	173,000	[2]
Unsecured Credit Facility, Fair Value	$ 185,747		$ 173,000

[1] We entered into interest rate protection agreements, with an aggregate notional value of $200,000, to effectively convert the variable rate to a fixed rate. See Note 13.

[2] The maturity date may be extended an additional year at our election, subject to certain restrictions.