Commitments and Contingencies - Narrative (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) ground_lease_extension_options	Dec. 31, 2018 USD ($)	Jan. 01, 2019 USD ($)
Long-term Purchase Commitment [Line Items]
Commitments for contracts and executed leases, operating and redevelopment and development properties	$ 1,200,000
Weighted average discount rate, ground leases	5.15%
Operating right of use ground lease asset	$ 82,794		$ 82,938
Operating ground lease liabilities	$ 87,247		$ 87,409
Weighted average remaining lease term	52 years
Variable lease, cost	$ 700
Period after which ground lease rentals are adjusted based on fair market value and the Consumer Price Index	5 years	5 years
Annual ground lease rental obligations limit	$ 1,000	$ 1,000
Average annual percentage rent for previous five years (percent)	50.00%	50.00%
Duration of ground lease prior to increase ten years	10 years
Average annual percentage rent for previous ten years (percent)	60.00%	60.00%
Environmental matters [Member]
Long-term Purchase Commitment [Line Items]
Accrued environmental remediation liabilities	$ 74,400
Ten year ground lease extension option [Member]
Long-term Purchase Commitment [Line Items]
Number of extension options | ground_lease_extension_options	3
Ground lease extension option term		10 years
Forty-five year ground lease extension option [Member]
Long-term Purchase Commitment [Line Items]
Number of extension options | ground_lease_extension_options	1
Ground lease extension option term	45 years