Debt - Summary of Mortgages, Notes Payable and Capital Lease Obligation (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Debt Disclosure [Abstract]
Senior unsecured notes	$ 535,000	$ 535,000
Unsecured term loan facilities	210,000	210,000
Fixed rate mortgages	158,337	160,718
Unsecured revolving credit facility	149,000	86,000
Junior subordinated notes	28,125	28,125
Subtotal debt	1,080,462	1,019,843
Unamortized premium	4,251	5,120
Unamortized deferred financing costs	(3,203)	(3,740)
Total debt	1,081,510	1,021,223
Capital lease obligation	$ 1,066	$ 1,066