Leases ASC 840 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating leases, scheduled future minimum payments receivable [Abstract]
Operating leases, scheduled future minimum payments receivable, 2019	$ 618,014
Operating leases, scheduled future minimum payments receivable, 2020	581,399
Operating leases, scheduled future minimum payments receivable, 2021	524,381
Operating leases, scheduled future minimum payments receivable, 2022	488,157
Operating leases, scheduled future minimum payments receivable, 2023	428,461
Operating leases, scheduled future minimum payments receivable, thereafter	2,068,891
Operating leases, total future minimum payments receivable due	4,709,303
Leases, Operating [Abstract]
Total rental property expense recorded for operating ground leases	2,500	$ 2,500	$ 2,900
Operating ground leases, scheduled future minimum payments [Abstract]
Operating ground leases, future minimum payments, 2019	2,184
Operating ground leases, future minimum payments, 2020	2,223
Operating ground leases, future minimum payments, 2021	2,263
Operating ground leases, future minimum payments, 2022	2,305
Operating ground leases, future minimum payments, 2023	2,308
Operating ground leases, future minimum payments, thereafter	86,577
Operating ground leases, total future minimum payments due	$ 97,860