Leases (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) property	Jun. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Fixed and in-substance fixed lease income	$ 197,413		$ 399,291
Variable lease income	62,610		125,445
Above/below market rent amortization			(19,496)	$ (19,326)
Uncollectible amounts in lease income	(580)		(1,444)
Total lease income	266,236	$ 272,203	543,539	539,713
Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year	389,051		389,051			$ 761,151
Lessor, Operating Lease, Payments to be Received, Two Years	735,879		735,879			693,848
Lessor, Operating Lease, Payments to be Received, Three Years	653,515		653,515			608,587
Lessor, Operating Lease, Payments to be Received, Four Years	561,918		561,918			516,369
Lessor, Operating Lease, Payments to be Received, Five Years	460,749		460,749			414,424
Lessor, Operating Lease, Payments to be Received, Thereafter	1,841,436		1,841,436			1,691,203
Lessor, Operating Lease, Payments to be Received	$ 4,642,548		$ 4,642,548			4,685,582
Number of Properties Subject to Ground Leases | property	22		22
Last Ground Lease Expiration Date			2101
Last Office Lease Expiration Date			2029
Operating Lease, Expense	$ 5,167	$ 5,000	$ 10,453	$ 9,200
Variable Lease, Cost	575		1,147
Operating cash flows from operating leases	3,721		7,412
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	7,858		7,858
Lessee, Operating Lease, Liability, Payments, Due Year Two	15,682		15,682
Lessee, Operating Lease, Liability, Payments, Due Year Three	14,537		14,537
Lessee, Operating Lease, Liability, Payments, Due Year Four	13,591		13,591
Lessee, Operating Lease, Liability, Payments, Due Year Five	13,102		13,102
Lessee, Operating Lease, Liability, Payments, Due after Year Five	570,036		570,036
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	634,806		634,806
Lessee, Operating Lease, Present Value Discount	(410,847)		(410,847)
Lease liabilities	223,959		223,959		$ 225,400	0
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 amortization	6,793		20,247
Ground Lease [Member]
Operating Leased Assets [Line Items]
Operating Lease, Expense	3,528		7,200
Variable Lease, Cost	444		873
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	5,336		5,336
Lessee, Operating Lease, Liability, Payments, Due Year Two	10,706		10,706
Lessee, Operating Lease, Liability, Payments, Due Year Three	10,674		10,674
Lessee, Operating Lease, Liability, Payments, Due Year Four	10,698		10,698
Lessee, Operating Lease, Liability, Payments, Due Year Five	10,914		10,914
Lessee, Operating Lease, Liability, Payments, Due after Year Five	564,081		564,081
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	612,409		612,409
Lessee, Operating Lease, Present Value Discount	(408,464)		(408,464)
Lease liabilities	$ 203,945		$ 203,945
Operating Lease, Weighted Average Discount Rate, Percent	5.20%		5.20%
Operating Lease, Weighted Average Remaining Lease Term	49 years 7 months 6 days		49 years 7 months 6 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	$ 1,064		$ 2,106
Variable Lease, Cost	131		274
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	2,522		2,522
Lessee, Operating Lease, Liability, Payments, Due Year Two	4,976		4,976
Lessee, Operating Lease, Liability, Payments, Due Year Three	3,863		3,863
Lessee, Operating Lease, Liability, Payments, Due Year Four	2,893		2,893
Lessee, Operating Lease, Liability, Payments, Due Year Five	2,188		2,188
Lessee, Operating Lease, Liability, Payments, Due after Year Five	5,955		5,955
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	22,397		22,397
Lessee, Operating Lease, Present Value Discount	(2,383)		(2,383)
Lease liabilities	$ 20,014		$ 20,014
Operating Lease, Weighted Average Discount Rate, Percent	4.00%		4.00%
Operating Lease, Weighted Average Remaining Lease Term	5 years 8 months 12 days		5 years 8 months 12 days
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	$ 4,592		$ 9,306