Leases (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) property	Sep. 30, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Operating Leased Assets [Line Items]
Fixed and in-substance fixed lease income	$ 203,407		$ 602,698
Variable lease income	59,872		185,317
Above/below market rent amortization			(30,196)	$ (26,031)
Uncollectible amounts in lease income	(2,222)		(3,667)
Total lease income	272,143	$ 268,948	815,682	808,661
Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year	198,877		198,877			$ 761,151
Lessor, Operating Lease, Payments to be Received, Two Years	765,960		765,960			693,848
Lessor, Operating Lease, Payments to be Received, Three Years	685,457		685,457			608,587
Lessor, Operating Lease, Payments to be Received, Four Years	593,471		593,471			516,369
Lessor, Operating Lease, Payments to be Received, Five Years	489,035		489,035			414,424
Lessor, Operating Lease, Payments to be Received, Thereafter	1,925,998		1,925,998			1,691,203
Lessor, Operating Lease, Payments to be Received	$ 4,658,798		$ 4,658,798			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	$ 5,081	$ 5,000	$ 15,533	$ 14,200
Variable Lease, Cost	501		1,646
Operating cash flows for operating leases	3,684		11,096
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	3,949		3,949
Lessee, Operating Lease, Liability, Payments, Due Year Two	15,786		15,786
Lessee, Operating Lease, Liability, Payments, Due Year Three	14,643		14,643
Lessee, Operating Lease, Liability, Payments, Due Year Four	13,700		13,700
Lessee, Operating Lease, Liability, Payments, Due Year Five	13,215		13,215
Lessee, Operating Lease, Liability, Payments, Due after Year Five	570,424		570,424
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	631,717		631,717
Lessee, Operating Lease, Present Value Discount	(408,136)		(408,136)
Lease liabilities	223,581		223,581		$ 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	11,086		31,334
Ground Lease [Member]
Operating Leased Assets [Line Items]
Operating Lease, Expense	3,514		10,714
Variable Lease, Cost	364		1,236
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	2,668		2,668
Lessee, Operating Lease, Liability, Payments, Due Year Two	10,707		10,707
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	564,080		564,080
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	609,741		609,741
Lessee, Operating Lease, Present Value Discount	(405,850)		(405,850)
Lease liabilities	$ 203,891		$ 203,891
Operating Lease, Weighted Average Discount Rate, Percent	5.20%		5.20%
Operating Lease, Weighted Average Remaining Lease Term	49 years 4 months 24 days		49 years 4 months 24 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	$ 1,066		$ 3,173
Variable Lease, Cost	137		410
Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year	1,281		1,281
Lessee, Operating Lease, Liability, Payments, Due Year Two	5,079		5,079
Lessee, Operating Lease, Liability, Payments, Due Year Three	3,969		3,969
Lessee, Operating Lease, Liability, Payments, Due Year Four	3,002		3,002
Lessee, Operating Lease, Liability, Payments, Due Year Five	2,301		2,301
Lessee, Operating Lease, Liability, Payments, Due after Year Five	6,344		6,344
Lessee, Operating Lease, Total Undiscounted Lease Liabilities	21,976		21,976
Lessee, Operating Lease, Present Value Discount	(2,286)		(2,286)
Lease liabilities	$ 19,690		$ 19,690
Operating Lease, Weighted Average Discount Rate, Percent	3.90%		3.90%
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	$ 4,580		$ 13,887