Investments in Real Estate (Narrative) (Details) ft² in Thousands, $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($) a customer property	Mar. 31, 2018 USD ($) ft² customer property	Dec. 31, 2018 ft²	Mar. 31, 2019 property	Mar. 31, 2019 ft²
Finite-Lived Intangible Assets [Line Items]
Revenues	$ 40,880	$ 37,107
Net income	15,532	10,057
Capitalized interest associated with redevelopment activities	$ 800	200
Improved land parcels [Member]
Finite-Lived Intangible Assets [Line Items]
Number of buildings | property				18
Area of real estate property	2.0				12,900
Redevelopment property [Member]
Finite-Lived Intangible Assets [Line Items]
Number of buildings | property				4
Area of real estate property	74.9				600
Asset acquisition, consideration transferred	$ 126,100
Asset acquisition, real estate development costs	48,100
Asset Acquisitions 2019 [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, assets acquired and liabilities assumed, net	68,200
Finite-lived intangible assets acquired	3,900
Asset acquisition, intangible liabilities	(3,300)
Revenues	200
Net income	100
Asset Acquisitions 2019 [Member] | Woodside [Member]
Finite-Lived Intangible Assets [Line Items]
Area of real estate property | ft²					65
Asset acquisition, consideration transferred	$ 10,000
Asset Acquisitions 2019 [Member] | Industrial building [Member]
Finite-Lived Intangible Assets [Line Items]
Number of properties acquired | property	2
Area of real estate property acquired | ft²			46
Asset Acquisitions 2019 [Member] | Improved land parcels [Member]
Finite-Lived Intangible Assets [Line Items]
Number of properties acquired | customer	2
Area of real estate property acquired | a	19.7
Asset Acquisitions 2019 [Member] | Land [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, property additions	$ 59,600
Asset Acquisitions 2019 [Member] | Building [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, property additions	$ 4,700
Asset Acquisitions 2018 [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, assets acquired and liabilities assumed, net		87,900
Finite-lived intangible assets acquired		2,600
Asset acquisition, intangible liabilities		2,300
Revenues		300
Net income		$ 200
Asset Acquisitions 2018 [Member] | Industrial building [Member]
Finite-Lived Intangible Assets [Line Items]
Number of properties acquired | customer		3
Area of real estate property acquired | ft²		418
Asset Acquisitions 2018 [Member] | Improved land parcels [Member]
Finite-Lived Intangible Assets [Line Items]
Number of properties acquired | property		2
Area of real estate property acquired | ft²		318
Asset Acquisitions 2018 [Member] | Land [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, property additions		$ 63,600
Asset Acquisitions 2018 [Member] | Building [Member]
Finite-Lived Intangible Assets [Line Items]
Asset acquisition, property additions		$ 21,700