Real Estate Investments - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
2017 Acquisitions [Member]
Real estate investments, at cost:
Land	$ 24,107
Buildings, fixtures and improvements	59,261
Total tangible assets	83,368
Assumed intangible liabilities:
Total purchase price of assets acquired	101,914
2017 Acquisitions [Member] | In-place leases [Member]
Acquired intangible assets:
Acquired intangible assets	15,916
2017 Acquisitions [Member] | Above-market leases [Member]
Acquired intangible assets:
Acquired intangible assets	2,815
2017 Acquisitions [Member] | Below-market leases [Member]
Assumed intangible liabilities:
Below-market leases	$ (185)
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 [Member]
Acquired intangible assets:
Acquired intangible assets		1,182
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