Real Estate Investments and Related Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Intangible lease assets:
Intangible lease assets, net	$ 1,233,062	$ 1,346,758
Intangible lease liabilities:
Accumulated amortization	$ 85,844	73,916
Weighted-Average Useful Life	18 years 7 months 20 days
Intangible lease liabilities, net	$ 179,192	198,551
In-place leases and other intangible assets [Member]
Intangible lease assets:
Weighted-Average Useful Life	15 years 4 months 28 days
Intangible lease assets, net	$ 1,006,399	1,091,433
Accumulated amortization	$ 680,775	599,680
Leasing Commissions [Member]
Intangible lease assets:
Weighted-Average Useful Life	10 years 11 months 16 days
Intangible lease assets, net	$ 13,547	13,876
Accumulated amortization	$ 3,526	2,902
Above-Market Leases [Member]
Intangible lease assets:
Weighted-Average Useful Life	16 years 4 months 13 days
Intangible lease assets, net	$ 213,116	241,449
Accumulated amortization	$ 102,355	$ 88,335