Schedule III: Real Estate and Accumulated Depreciation (Parenthetical) (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Property		Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	488
Tenant improvements, useful life	Lease Term
Balance, Beginning of Year	$ 3,388,611		$ 3,297,649	$ 3,183,369
Acquisition of Real Estate Assets	168,517		108,538	161,074
Construction Costs and Improvements	137,361		167,342	142,535
Disposition of Real Estate Assets	(170,928)		(153,364)	(162,636)
Impairment of Real Estate	0		0	(626)
Write-off of Fully Depreciated and Other Assets	(27,816)		(31,554)	(26,067)
Balance, End of Year Including Real Estate Held for Sale	3,495,745		3,388,611	3,297,649
Real Estate Held for Sale	0	[1]	(3,697)	(3,681)
Balance, End of Year Excluding Real Estate Held for Sale	3,495,745		3,384,914	3,293,968
Balance, Beginning of Year	797,919		792,501	786,978
Depreciation for Year	94,078		95,514	92,955
Disposition of Assets	(78,844)		(62,634)	(61,365)
Write-off of Fully Depreciated and Other Assets	(23,234)		(27,462)	(26,067)
Balance, End of Year Including Real Estate Held for Sale	789,919		797,919	792,501
Real Estate Held for Sale	0	[2]	(1,427)	(1,171)
Balance, End of Year Excluding Real Estate Held for Sale	$ 789,919		$ 796,492	$ 791,330
Buildings and Improvements | Minimum
Real Estate and Accumulated Depreciation [Line Items]
Property, plant and equipment, useful life	7 years
Buildings and Improvements | Maximum
Real Estate and Accumulated Depreciation [Line Items]
Property, plant and equipment, useful life	50 years
Land Improvements | Minimum
Real Estate and Accumulated Depreciation [Line Items]
Property, plant and equipment, useful life	5 years
Land Improvements | Maximum
Real Estate and Accumulated Depreciation [Line Items]
Property, plant and equipment, useful life	20 years
5570 Tulane Dr [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 1,976
825-827 Avenue H [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 1,603
1172-84 113th Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 1,312
1200-16 Avenue H [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 1,295
8200 East Park Meadows Drive [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 3,666
3250 Quentin Street [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 3,311
1908-2000 Innerbelt [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	2
Balance, End of Year Including Real Estate Held for Sale	$ 4,783
1322-66 W. North Carrier Parkway [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	3
Balance, End of Year Including Real Estate Held for Sale	$ 2,469
Plano Crossing Bus. Park [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	4
Balance, End of Year Including Real Estate Held for Sale	$ 4,611
801-831 S Great Southwest Pkwy [Member]
Real Estate and Accumulated Depreciation [Line Items]
Number of industrial properties | Property	5
Balance, End of Year Including Real Estate Held for Sale	$ 10,466

[1] The Real Estate Held for Sale at December 31, 2017 excludes $0 of other assets.

[2] The Real Estate Held for Sale at December 31, 2017 excludes $0 of accumulated amortization related to the other assets mentioned above.