Indebtedness - Summary of Indebtedness at Estimated Fair Value (Detail) - USD ($) $ in Thousands		Sep. 30, 2015	Dec. 31, 2014
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount		$ 590,912	$ 599,985
Senior Unsecured Notes, Net, Carrying Amount		364,932	364,861
Unsecured Term Loan, Carrying Amount		460,000	200,000
Unsecured Credit Facility, Carrying Amount		55,000	185,000
Total, Carrying Amount		1,470,844	1,349,846
Total, Fair Value		1,534,206	1,422,460
Mortgage Loans Payable, Net
Debt Disclosure [Line Items]
Mortgage Loans Payable, Net, Carrying Amount		590,912	599,985
Mortgage Loans Payable, Net, Fair Value		632,104	640,818
Senior Unsecured Notes, Net
Debt Disclosure [Line Items]
Senior Unsecured Notes, Net, Carrying Amount		364,932	364,861
Senior Unsecured Notes, Net, Fair Value		386,086	395,320
Unsecured Term Loans
Debt Disclosure [Line Items]
Unsecured Term Loan, Carrying Amount		460,000	200,000
Unsecured Term Loan, Fair Value		461,016	200,575
Unsecured Credit Facility
Debt Disclosure [Line Items]
Unsecured Credit Facility, Carrying Amount	[1]	55,000	185,000
Unsecured Credit Facility, Fair Value		$ 55,000	$ 185,747

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