Real Estate Investment and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Balance at beginning of year	$ 2,510,579	$ 2,488,361	$ 2,436,266
Acquisitions			33,077
Improvements	21,899	22,302	19,150
Disposals	(2,837)	(84)	(132)
Balance at end of year	2,529,641	2,510,579	2,488,361
Balance at beginning of year	754,861	691,691	629,292
Depreciation	63,718	63,180	62,492
Disposals	(256)	(10)	(93)
Balance at end of year	$ 818,323	$ 754,861	$ 691,691