Reconciliation of Real Estate Properties and Accumulated Depreciation (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate And Accumulated Depreciation Disclosure [Abstract]
Beginning balance		$ 585,828	$ 511,657	$ 486,589
Additions	[1]	12,492	14,186	4,972
Acquisitions		9,931	60,031	24,568
Disposals/Divestitures	[2]	(8,475)	(46)	(4,472)
Ending balance		599,776	585,828	511,657
Beginning balance		138,588	121,161	106,480
Disposals/Divestitures	[2]	(4,896)	(9)	(1,568)
Depreciation expense		19,687	17,436	16,249
Ending balance		$ 153,379	$ 138,588	$ 121,161

[1] Included in the additions during 2017 and 2016, were $3.0 million and $9.5 million, respectively, related to Henderson Medical Plaza, which was completed and opened during 2017.

[2] 2017 includes property damage write-downs resulting from substantial damage from Hurricane Harvey during the third quarter of 2017, as discussed in Note 10 to the consolidated financial statements – Impact of Hurricane Harvey.