Allocation of Purchase Price to Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
2017 Acquisitions
Business Acquisition [Line Items]
Land	$ 1,496
Buildings and improvements	8,434
Intangible assets	1,598
Below-market lease intangibles	(2,488)
Net cash paid	$ 9,040
2016 Acquisitions
Business Acquisition [Line Items]
Land		$ 9,914
Buildings and improvements		50,117
Intangible assets		9,211
Below-market lease intangibles		(1,287)
Deposit paid		(150)
Debt (including fair value adjustment of $362)		(7,499)
Financing fees paid on debt acquired		83
Net cash paid		$ 60,389
2015 Acquisitions
Business Acquisition [Line Items]
Land			$ 7,050
Buildings and improvements			17,518
Intangible assets			2,182
Cash received- exchange transaction			2,000
Other liabilities			(116)
Deposit paid			(100)
Net book value of property divested in exchange transaction			(3,027)
Gain on exchange transaction			(8,742)
Net cash paid			$ 16,765