Identified Intangible Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets and Liabilities
Gross amount	$ 307,855		$ 307,855		$ 310,097
Accumulated amortization	(167,861)		(167,861)		(150,837)
Total, net	139,994		139,994		159,260
Gross amount	508,468		508,468		530,497
Accumulated amortization	(338,665)		(338,665)		(324,897)
Total, net	169,803		169,803		$ 205,600
Below Market Leases Net Of Above Market Leases
Finite-Lived Intangible Assets and Liabilities
Increase to rental income	10,373	$ 11,054	31,480	$ 34,758
2019	25,115		25,115
2020	24,047		24,047
2021	19,313		19,313
2022	16,173		16,173
2023	13,496		13,496
Other Identified Intangible Assets
Finite-Lived Intangible Assets and Liabilities
Amortization of Intangible Assets	4,822	6,069	14,557	19,896
2019	12,902		12,902
2020	12,817		12,817
2021	11,838		11,838
2022	10,286		10,286
2023	10,158		10,158
Tenant Under Ground Leases
Finite-Lived Intangible Assets and Liabilities
Increase to rent expense	437	$ 437	1,310	$ 1,310
2019	1,747		1,747
2020	1,747		1,747
2021	1,747		1,747
2022	1,747		1,747
2023	$ 1,747		$ 1,747