Real Estate Investments - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Assumed intangible liabilities:
Below market lease, weighted average useful life	18 years 4 months 26 days
In-place leases and other intangible assets [Member]
Assumed intangible liabilities:
Weighted-Average Useful Life	15 years 23 days
Above-market leases [Member]
Assumed intangible liabilities:
Weighted-Average Useful Life	16 years 2 months 28 days
2017 Acquisitions [Member]
Real estate investments, at cost:
Land	$ 82,337
Buildings, fixtures and improvements	293,419
Total tangible assets	375,756
Assumed intangible liabilities:
Total purchase price of assets acquired	453,937
2017 Acquisitions [Member] | In-place leases and other intangible assets [Member]
Acquired intangible assets:
Acquired intangible assets	$ 68,306
Assumed intangible liabilities:
Weighted-Average Useful Life	16 years 8 months 9 days
2017 Acquisitions [Member] | Above-market leases [Member]
Acquired intangible assets:
Acquired intangible assets	$ 10,270
Assumed intangible liabilities:
Weighted-Average Useful Life	18 years 1 month 21 days
2017 Acquisitions [Member] | Below-market leases [Member]
Assumed intangible liabilities:
Below-market leases	$ (395)
Below market lease, weighted average useful life	19 years 11 months 16 days
2016 Acquisitions [Member]
Real estate investments, at cost:
Land		$ 4,215
Buildings, fixtures and improvements		14,555
Total tangible assets		18,770
Assumed intangible liabilities:
Total purchase price of assets acquired		19,952
2016 Acquisitions [Member] | In-place leases and other intangible assets [Member]
Acquired intangible assets:
Acquired intangible assets		$ 1,182
Assumed intangible liabilities:
Weighted-Average Useful Life		14 years 6 months
2016 Acquisitions [Member] | Above-market leases [Member]
Acquired intangible assets:
Acquired intangible assets		$ 0
2016 Acquisitions [Member] | Below-market leases [Member]
Assumed intangible liabilities:
Below-market leases		$ 0