Identified Intangible Assets and Liabilities (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets and Liabilities
Gross amount	$ 309,776,000		$ 309,776,000		$ 310,097,000
Accumulated amortization	(163,406,000)		(163,406,000)		(150,837,000)
Total, net	146,370,000		146,370,000		159,260,000
Gross amount	527,766,000		527,766,000		530,497,000
Accumulated amortization	(346,474,000)		(346,474,000)		(324,897,000)
Total, net	181,292,000		181,292,000		$ 205,600,000
Below Market Leases Net Of Above Market Leases
Finite-Lived Intangible Assets and Liabilities
Increase to rental income	10,526,000	$ 12,588,000	21,107,000	$ 23,704,000
2019	29,871,000		29,871,000
2020	22,213,000		22,213,000
2021	17,478,000		17,478,000
2022	14,339,000		14,339,000
2023	11,661,000		11,661,000
Other Identified Intangible Assets
Finite-Lived Intangible Assets and Liabilities
Amortization of Intangible Assets	4,876,000	6,846,000	9,735,000	13,827,000
2019	14,994,000		14,994,000
2020	12,008,000		12,008,000
2021	11,030,000		11,030,000
2022	9,477,000		9,477,000
2023	9,349,000		9,349,000
Tenant Under Ground Leases
Finite-Lived Intangible Assets and Liabilities
Increase to rent expense	437,000	$ 437,000	874,000	$ 874,000
2019	1,747,000		1,747,000
2020	1,747,000		1,747,000
2021	1,747,000		1,747,000
2022	1,747,000		1,747,000
2023	$ 1,747,000		$ 1,747,000