Indebtedness - Summary of Indebtedness at Estimated Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	$ 596,998		$ 599,985
Senior Unsecured Notes, Net, Carrying Amount	364,885		364,861
Unsecured Term Loan, Carrying Amount	200,000		200,000
Unsecured Credit Facility, Carrying Amount	168,000		185,000
Total, Carrying Amount	1,329,883		1,349,846
Total, Fair Value	1,402,866		1,422,460
Mortgage Loans Payable, Net
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount	596,998		599,985
Mortgage Loans Payable, Net, Fair Value	641,253		640,818
Senior Unsecured Notes, Net
Debt Disclosure [Line Items]
Senior Unsecured Notes, Net, Carrying Amount	364,885		364,861
Senior Unsecured Notes, Net, Fair Value	393,061		395,320
Unsecured Term Loan
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount	200,000	[1]	200,000	[1]
Unsecured Term Loan, Fair Value	200,552		200,575
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	168,000	[2]	185,000	[2]
Unsecured Credit Facility, Fair Value	$ 168,000		$ 185,747

[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 10.

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