Leases (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Jan. 01, 2019 USD ($)
Operating Leased Assets [Line Items]
Fixed and in-substance fixed lease income	$ 806,442
Variable lease income	247,861
Uncollectible amounts in lease income	(5,394)
Total lease income	1,094,301	$ 1,083,770	$ 950,186
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	775,723	761,151
Lessor, Operating Lease, Payments to be Received, Two Years	706,016	693,848
Lessor, Operating Lease, Payments to be Received, Three Years	615,224	608,587
Lessor, Operating Lease, Payments to be Received, Four Years	511,104	516,369
Lessor, Operating Lease, Payments to be Received, Five Years	411,308	414,424
Lessor, Operating Lease, Payments to be Received, Thereafter	1,500,745	1,691,203
Lessor, Operating Lease, Payments to be Received	$ 4,520,120	4,685,582
Number of Properties Subject to Ground Leases | property	22
Last Ground Lease Expiration Date	2101
Last Office Lease Expiration Date	2029
Operating Lease, Expense	$ 20,456	19,100	$ 18,400
Variable Lease, Cost	2,245
Operating cash flows for operating leases	14,815
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	15,849
Lessee, Operating Lease, Liability, Payments, Due Year Two	14,820
Lessee, Operating Lease, Liability, Payments, Due Year Three	13,886
Lessee, Operating Lease, Liability, Payments, Due Year Four	13,325
Lessee, Operating Lease, Liability, Payments, Due Year Five	12,903
Lessee, Operating Lease, Liability, Payments, Due after Year Five	557,520
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	628,303
Lessee, Operating Lease, Present Value Discount	(405,385)
Lease liabilities	222,918	0		$ 225,400
Operating Leases, Future Minimum Payments Due, Next Twelve Months		15,077
Operating Leases, Future Minimum Payments, Due in Two Years		14,733
Operating Leases, Future Minimum Payments, Due in Three Years		13,893
Operating Leases, Future Minimum Payments, Due in Four Years		13,151
Operating Leases, Future Minimum Payments, Due in Five Years		12,558
Operating Leases, Future Minimum Payments, Due Thereafter		467,706
Operating Leases, Future Minimum Payments Due		537,118
Lessor [Member]
Operating Leased Assets [Line Items]
Above/below market rent and tenant rent inducement amortization	45,392
Ground Lease [Member]
Operating Leased Assets [Line Items]
Operating Lease, Expense	13,982
Variable Lease, Cost	1,693
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	10,697
Lessee, Operating Lease, Liability, Payments, Due Year Two	10,671
Lessee, Operating Lease, Liability, Payments, Due Year Three	10,698
Lessee, Operating Lease, Liability, Payments, Due Year Four	10,915
Lessee, Operating Lease, Liability, Payments, Due Year Five	10,964
Lessee, Operating Lease, Liability, Payments, Due after Year Five	553,116
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	607,061
Lessee, Operating Lease, Present Value Discount	(403,237)
Lease liabilities	$ 203,824
Operating Lease, Weighted Average Discount Rate, Percent	5.20%
Operating Lease, Weighted Average Remaining Lease Term	49 years 2 months 12 days
Operating Leases, Future Minimum Payments Due, Next Twelve Months		10,672
Operating Leases, Future Minimum Payments, Due in Two Years		10,439
Operating Leases, Future Minimum Payments, Due in Three Years		10,344
Operating Leases, Future Minimum Payments, Due in Four Years		10,258
Operating Leases, Future Minimum Payments, Due in Five Years		10,369
Operating Leases, Future Minimum Payments, Due Thereafter		461,762
Operating Leases, Future Minimum Payments Due		513,844
Office Lease [Member]
Operating Leased Assets [Line Items]
Operating Lease, Expense	$ 4,229
Variable Lease, Cost	552
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	5,152
Lessee, Operating Lease, Liability, Payments, Due Year Two	4,149
Lessee, Operating Lease, Liability, Payments, Due Year Three	3,188
Lessee, Operating Lease, Liability, Payments, Due Year Four	2,410
Lessee, Operating Lease, Liability, Payments, Due Year Five	1,939
Lessee, Operating Lease, Liability, Payments, Due after Year Five	4,404
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	21,242
Lessee, Operating Lease, Present Value Discount	(2,148)
Lease liabilities	$ 19,094
Operating Lease, Weighted Average Discount Rate, Percent	3.90%
Operating Lease, Weighted Average Remaining Lease Term	5 years 6 months
Operating Leases, Future Minimum Payments Due, Next Twelve Months		4,405
Operating Leases, Future Minimum Payments, Due in Two Years		4,294
Operating Leases, Future Minimum Payments, Due in Three Years		3,549
Operating Leases, Future Minimum Payments, Due in Four Years		2,893
Operating Leases, Future Minimum Payments, Due in Five Years		2,189
Operating Leases, Future Minimum Payments, Due Thereafter		5,944
Operating Leases, Future Minimum Payments Due		$ 23,274
Fixed Lease Expense [Member]
Operating Leased Assets [Line Items]
Operating Lease, Expense	$ 18,211