Real Estate Investments and Related Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Intangible lease assets:
Intangible lease assets, net	$ 1,311,209	$ 1,346,758
Intangible lease liabilities:
Accumulated amortization	$ 78,738	73,916
Weighted-Average Useful Life	18 years 7 months
Intangible lease liabilities, net	$ 193,703	198,551
In-place leases and other intangible assets [Member]
Intangible lease assets:
Weighted-Average Useful Life	15 years 2 months 1 day
Intangible lease assets, net	$ 1,064,366	1,091,433
Accumulated amortization	$ 628,165	599,679
Leasing Commissions [Member]
Intangible lease assets:
Weighted-Average Useful Life	11 years 1 month
Intangible lease assets, net	$ 13,741	13,876
Accumulated amortization	$ 3,279	2,902
Above-Market Leases [Member]
Intangible lease assets:
Weighted-Average Useful Life	16 years 3 months
Intangible lease assets, net	$ 233,102	241,449
Accumulated amortization	$ 92,351	$ 88,335