Real Estate Investments and Related Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Intangible lease assets:
Intangible lease assets, net	$ 1,346,758	$ 1,478,884
Intangible lease liabilities:
Accumulated amortization	$ 73,916	56,891
Weighted-Average Useful Life	18 years 8 months 14 days
Intangible lease liabilities, net	$ 198,551	224,023
In-place leases and other intangible assets [Member]
Intangible lease assets:
Weighted-Average Useful Life	15 years 1 month 25 days
Intangible lease assets, net	$ 1,091,433	1,192,756
Accumulated amortization	$ 599,680	494,131
Leasing Commissions [Member]
Intangible lease assets:
Weighted-Average Useful Life	10 years 6 months 30 days
Intangible lease assets, net	$ 13,876	10,231
Accumulated amortization	$ 2,902	1,836
Above-Market Leases [Member]
Intangible lease assets:
Weighted-Average Useful Life	16 years 3 months 17 days
Intangible lease assets, net	$ 241,449	275,897
Accumulated amortization	$ 88,335	$ 69,670