Indebtedness - Additional Information (Details) $ in Thousands, ft² in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018 USD ($) ft² Property	Jun. 30, 2017 USD ($)	Jun. 30, 2018 USD ($) ft² Property	Jun. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Debt Instrument [Line Items]
Number of industrial properties | Property		471		471
Gross leasable area (GLA) of industrial properties | ft²		61.1		61.1
Loss from Retirement of Debt		$ 0	$ 0	$ (39)	$ (1,653)
Long-term Debt, Gross		1,309,863		1,309,863
Unsecured Credit Facility
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		4,182		4,182		$ 4,781
Mortgage Loans Payable
Debt Instrument [Line Items]
Unamortized Debt Issuance Costs		1,490		1,490		1,806
Extinguishment of debt, amount				157,782
Loss from Retirement of Debt				39
Net carrying value of industrial properties collateralized by mortgage loans		450,187		450,187
Long-term Debt, Gross		$ 301,292		$ 301,292		451,602
2014 Unsecured Term Loan
Debt Instrument [Line Items]
Debt Instrument Interest Rate Change Due to Investment Grade Rating				10 basis point
Interest Rate	[1]	3.39%		3.39%
Long-term Debt, Gross		$ 200,000		$ 200,000		200,000
2015 Unsecured Term Loan
Debt Instrument [Line Items]
Debt Instrument Interest Rate Change Due to Investment Grade Rating				10 basis point
Interest Rate	[1]	2.89%		2.89%
Long-term Debt, Gross		$ 260,000		$ 260,000		260,000
Assumed Mortgage | Mortgage Loans Payable
Debt Instrument [Line Items]
Assumed Mortgage Loan				$ 11,654
Number of industrial properties | Property		3		3
Gross leasable area (GLA) of industrial properties | ft²		0.2		0.2
Interest Rate		4.17%		4.17%
2028 Private Placement Notes
Debt Instrument [Line Items]
Interest Rate		3.86%		3.86%
Long-term Debt, Gross		$ 150,000		$ 150,000		0
Effective Interest Rate		3.86%		3.86%
2030 Private Placement Notes
Debt Instrument [Line Items]
Interest Rate		3.96%		3.96%
Long-term Debt, Gross		$ 150,000		$ 150,000		$ 0
Effective Interest Rate		3.96%		3.96%

[1] The interest rate at June 30, 2018 also reflects the interest rate protection agreements we entered into to effectively convert the variable rate to a fixed rate. See Note 10.