Rental Property - Acquisitions - Allocation of Consideration (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
In-place leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ 62,533	$ 58,109
Acquisitions 2016
Allocation of the consideration paid for the acquired assets and liabilities
Land	59,630
Buildings	283,758
Tenant improvements	8,670
Building and land Improvements	29,073
Below market leases	$ (12,971)
Acquired Below Market Leases, Weighted Average Useful Life	8 years 5 months 18 days
Above market assumed debt adjustment	$ (75)
Other assets	158
Total purchase price	471,798
Less: Mortgage notes assumed	(4,037)
Less: Contingent consideration	0
Net assets acquired	$ 467,761
Weighted average amortization period of above market debt adjustment	7 years 2 months
Acquisitions 2016 | In-place leases
Allocation of the consideration paid for the acquired assets and liabilities
Weighted average amortization period of lease intangibles	8 years 2 months 18 days
Acquisitions 2016 | Tenant relationships
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ 30,446
Weighted average amortization period of lease intangibles	10 years 4 months 18 days
Acquisitions 2016 | Above market leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles	$ 10,576
Weighted average amortization period of lease intangibles	9 years 2 months
2015 Acquisitions
Allocation of the consideration paid for the acquired assets and liabilities
Land		45,117
Buildings		256,970
Tenant improvements		7,705
Building and land Improvements		20,712
Below market leases		$ (4,022)
Acquired Below Market Leases, Weighted Average Useful Life		5 years 2 months 12 days
Above market assumed debt adjustment		$ (418)
Other assets		565
Total purchase price		427,263
Less: Mortgage notes assumed		(26,267)
Less: Contingent consideration		(300)
Net assets acquired		$ 400,696
Weighted average amortization period of above market debt adjustment		1 year 4 months 18 days
2015 Acquisitions | In-place leases
Allocation of the consideration paid for the acquired assets and liabilities
Weighted average amortization period of lease intangibles		5 years 6 months 20 days
2015 Acquisitions | Tenant relationships
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles		$ 31,390
Weighted average amortization period of lease intangibles		8 years
2015 Acquisitions | Above market leases
Allocation of the consideration paid for the acquired assets and liabilities
Deferred leasing intangibles		$ 11,135
Weighted average amortization period of lease intangibles		7 years 3 months 18 days