Schedule III - Changes in Accumulated Depreciation (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real estate held for sale	$ 146,615
Intangible lease assets	443,134		$ 296,176
Accumulated Depreciation	406,855	[1]	292,786	$ 232,675	$ 181,441
Accumulated amortization	48,857		$ 32,339
Real Estate Held For Sale [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Intangible lease assets	15,800
Accumulated Depreciation	500
Accumulated amortization	100
Real Estate Held For Sale [Member] | Land and Building [Member]
SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items]
Real estate held for sale	$ 131,400

[1] Includes accumulated depreciation in real estate held for sale of $0.5 million. Excludes accumulated amortization related to intangible lease assets that are included in real estate held for sale of $0.1 million for 2017.