Goodwill and Other Intangibles - Intangible Lease Assets and Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Intangible lease liabilities:
Accumulated amortization	$ 70,070	$ 56,891
Weighted-Average Useful Life	18 years 4 months 26 days
Intangible lease liabilities, net	$ 204,051	224,023
Total Intangible Lease Assets [Member]
Intangible lease assets:
Intangible lease assets, net	1,360,445	1,478,884
In-place leases and other intangible assets [Member]
Intangible lease assets:
Accumulated amortization	$ 580,588	494,131
Weighted-Average Useful Life	15 years 23 days
Intangible lease assets, net	$ 1,100,403	1,192,756
Leasing Commissions [Member]
Intangible lease assets:
Accumulated amortization	$ 2,601	1,836
Weighted-Average Useful Life	10 years 6 months 18 days
Intangible lease assets, net	$ 11,117	10,231
Above-Market Leases [Member]
Intangible lease assets:
Accumulated amortization	$ 83,670	69,670
Weighted-Average Useful Life	16 years 2 months 28 days
Intangible lease assets, net	$ 248,925	$ 275,897