Operating Leases (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)	Dec. 31, 2018 USD ($)
Property Subject to or Available for Operating Lease [Line Items]
Property operating expense	$ 15,793	$ 7,564
Operating Lease, Right-of-Use Asset	$ 211,299			$ 0
Number of Properties Subject to Ground Leases	57
General and Administrative Expense	$ 12,130	12,324
Operating Leases, Income Statement, Lease Revenue	(150,723)	(132,924)
Lease, Cost	445
Straight-Line Rent Receivable	98,372			73,332
Total Operating Leased Assets	235,937
Operating Lease, Liability	235,612			0
Operating Leases, Future Minimum Payments Receivable, Current	414,812
Operating Leases, Future Minimum Payments Receivable, in Two Years	538,038
Operating Leases, Future Minimum Payments Receivable, in Three Years	527,358
Operating Leases, Future Minimum Payments Receivable, in Four Years	512,295
Operating Leases, Future Minimum Payments Receivable, in Five Years	483,380
Operating Leases, Future Minimum Payments Receivable, Thereafter	4,331,678
Operating Leases, Future Minimum Payments Receivable	6,807,561
Ground Lease Arrangement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	398,100			520,139
Operating Leases, Future Minimum Payments Receivable, in Two Years	515,418			503,344
Operating Leases, Future Minimum Payments Receivable, in Three Years	504,422			492,165
Operating Leases, Future Minimum Payments Receivable, in Four Years	489,968			477,671
Operating Leases, Future Minimum Payments Receivable, in Five Years	461,749			449,686
Operating Leases, Future Minimum Payments Receivable, Thereafter	4,092,159			3,953,717
Operating Leases, Future Minimum Payments Receivable	$ 6,461,816			6,396,722
Ground Lease Arrangement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	17 years 5 months
Property operating expense	$ 5,938
Operating Lease, Right-of-Use Asset	205,626
Receivable with Imputed Interest, Discount	136,962
Operating Lease, Liability	$ 229,755
Operating Lease, Weighted Average Discount Rate, Percent	4.91%
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 17,125			22,867
Operating Leases, Future Minimum Payments, Due in Two Years	23,236			23,236
Operating Leases, Future Minimum Payments, Due in Three Years	23,600			23,600
Operating Leases, Future Minimum Payments, Due in Four Years	22,998			22,996
Operating Leases, Future Minimum Payments, Due in Five Years	22,304			22,303
Operating Leases, Future Minimum Payments, Due Thereafter	257,454			257,446
Operating Leases, Future Minimum Payments Due	366,717			372,448
Operating Leases, Future Minimum Payments Receivable, Current	16,712
Operating Leases, Future Minimum Payments Receivable, in Two Years	22,620
Operating Leases, Future Minimum Payments Receivable, in Three Years	22,936
Operating Leases, Future Minimum Payments Receivable, in Four Years	22,327
Operating Leases, Future Minimum Payments Receivable, in Five Years	21,631
Operating Leases, Future Minimum Payments Receivable, Thereafter	239,519
Operating Leases, Future Minimum Payments Receivable	$ 345,745
Office Lease [Member]
Property Subject to or Available for Operating Lease [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	7 years 6 months
Operating Lease, Right-of-Use Asset	$ 5,673
General and Administrative Expense	230
Receivable with Imputed Interest, Discount	1,117
Operating Lease, Liability	$ 5,857
Operating Lease, Weighted Average Discount Rate, Percent	4.62%
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 642			856
Operating Leases, Future Minimum Payments, Due in Two Years	856			856
Operating Leases, Future Minimum Payments, Due in Three Years	884			884
Operating Leases, Future Minimum Payments, Due in Four Years	967			967
Operating Leases, Future Minimum Payments, Due in Five Years	967			967
Operating Leases, Future Minimum Payments, Due Thereafter	2,658			2,658
Operating Leases, Future Minimum Payments Due	6,974			$ 7,188
sublease [Member]
Property Subject to or Available for Operating Lease [Line Items]
Operating Leases, Income Statement, Lease Revenue	$ (5,723)
Minimum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lessee, Operating Lease, Term of Contract	1 year
Minimum [Member] | Ground Lease Arrangement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lessee, Operating Lease, Term of Contract	2 years
Maximum [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lessee, Operating Lease, Term of Contract	31 years
Maximum [Member] | Ground Lease Arrangement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Lessee, Operating Lease, Term of Contract	47 years
Ground Lease Arrangement [Member]
Property Subject to or Available for Operating Lease [Line Items]
Straight-Line Rent Receivable	$ 24,638	$ 0	$ 24,454