Real Estate Investments and Related Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Intangible lease assets:
Intangible lease assets, net	$ 1,037,487	$ 1,198,506
Intangible lease liabilities:
Accumulated amortization	$ 99,315	89,905
Weighted-Average Useful Life	19 years 1 month 6 days
Intangible lease liabilities, net	$ 143,583	173,479
Amortization expense	$ 2,538	4,178	$ 5,366
In-place leases and other intangible assets [Member]
Intangible lease assets:
Weighted-Average Useful Life	15 years 10 months 24 days
Intangible lease assets, net	$ 854,196	980,971
Accumulated amortization	$ 748,689	703,909
Leasing commissions [Member]
Intangible lease assets:
Weighted-Average Useful Life	10 years 1 month 6 days
Intangible lease assets, net	$ 17,808	15,660
Accumulated amortization	$ 6,027	4,048
Above-market lease assets and deferred lease incentives [Member]
Intangible lease assets:
Weighted-Average Useful Life	16 years 3 months 18 days
Intangible lease assets, net	$ 165,483	201,875
Accumulated amortization	112,438	105,936
Above‑ And Below-Market Leases and Deferred Lease Incentives [Member]
Intangible lease liabilities:
Amortization expense	2,500	4,200	5,400
In-Place Leases, Leasing Commissions and Other Lease Intangibles [Member]
Intangible lease liabilities:
Amortization expense	$ 127,500	$ 139,600	$ 154,200