Reconciliation of Real Estate Properties and Accumulated Depreciation (Parenthetical) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Real Estate and Accumulated Depreciation [Line Items]
Additions	[1]	$ 12,492	$ 14,186	$ 4,972
Henderson Medical Plaza
Real Estate and Accumulated Depreciation [Line Items]
Additions		$ 3,000	$ 9,500

[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.