Real Estate Investment and Accumulated Depreciation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract]
Balance at beginning of year	$ 2,488,361	$ 2,436,266	$ 2,429,282
Acquisitions		33,077
Improvements	22,302	19,150	11,806
Disposals	(84)	(132)	(3,406)
Impairments			(1,416)
Balance at end of year	2,510,579	2,488,361	2,436,266
Balance at beginning of year	691,691	629,292	568,681
Depreciation	63,180	62,492	64,095
Disposals	(10)	(93)	(3,484)
Balance at end of year	$ 754,861	$ 691,691	$ 629,292