Indebtedness - Summary of Indebtedness at Estimated Fair Value (Detail) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount		$ 593,976	$ 599,985
Senior Unsecured Notes, Net, Carrying Amount		364,908	364,861
Unsecured Term Loan, Carrying Amount		200,000	200,000
Unsecured Credit Facility, Carrying Amount		191,000	185,000
Total, Carrying Amount		1,349,884	1,349,846
Total, Fair Value		1,412,920	1,422,460
Mortgage Loans Payable, Net
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount		593,976	599,985
Mortgage Loans Payable, Net, Fair Value		630,655	640,818
Senior Unsecured Notes, Net
Debt Disclosure [Line Items]
Senior Unsecured Notes, Net, Carrying Amount		364,908	364,861
Senior Unsecured Notes, Net, Fair Value		390,735	395,320
Unsecured Term Loan
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount	[1]	200,000	200,000
Unsecured Term Loan, Fair Value		200,530	200,575
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	[2]	191,000	185,000
Unsecured Credit Facility, Fair Value		$ 191,000	$ 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.