Real Estate Investments and Related Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 731	$ 1,487
Intangible lease assets:
Intangible lease assets, net	1,158,938		$ 1,198,506
Intangible lease liabilities:
Accumulated amortization	$ 93,268		89,905
Weighted-Average Useful Life	18 years 10 months 24 days
Intangible lease liabilities, net	$ 166,708		173,479
In-place leases and other intangible assets [Member]
Intangible lease assets:
Weighted-Average Useful Life	15 years 6 months
Intangible lease assets, net	$ 948,973		980,971
Accumulated amortization	$ 730,221		703,909
Leasing Commissions [Member]
Intangible lease assets:
Weighted-Average Useful Life	10 years 4 months 24 days
Intangible lease assets, net	$ 16,318		15,660
Accumulated amortization	$ 4,566		4,048
Above-Market Lease assets and deferred lease incentives [Member]
Intangible lease assets:
Weighted-Average Useful Life	16 years 4 months 24 days
Intangible lease assets, net	$ 193,647		201,875
Accumulated amortization	110,100		$ 105,936
Above‑ And Below-Market Leases and Deferred Lease Incentives [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	700	1,500
In-Place Leases, Leasing Commissions and Other Lease Intangibles [Member]
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 33,800	$ 34,600