Summary of significant accounting policies (Details) $ in Thousands		3 Months Ended								12 Months Ended
	Jan. 01, 2019 USD ($)	Dec. 31, 2019 USD ($) property	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) property	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounting policies
Maximum expected period of sale of property (in years)										1 year
Cost method investment ownership percentage		10.00%								10.00%
Percentage of total revenues										95.90%
Write-off of lease origination costs that were capitalized in connection with leases executed prior to 1/1/19	$ 3,500
Ground and Operating Lease Obligation Due	590,300	$ 699,900								$ 699,900
Operating lease liability	218,700	271,808				$ 0				$ 271,808	$ 0
Reclassification of deferred rent liabilities	$ 27,000
Minimum percentage of taxable income to be distributed										90.00%
Percent of taxable income, generally distributed as dividend										100.00%
Long-term Debt		6,777,479								$ 6,777,479
Income from rentals
Operating leases income										1,465,692
Direct financing lease income										2,421
Revenues subject to the new lease accounting standard										1,468,113
Revenues		$ 408,114	$ 390,484	$ 373,856	$ 358,842	$ 340,463	$ 341,823	$ 325,034	$ 320,139	$ 1,531,296	1,327,459	$ 1,128,097
Maximum | Land improvements
Accounting policies
Estimated useful life										20 years
Maximum | Buildings and building improvements
Accounting policies
Estimated useful life										40 years
Canada
Accounting policies
Number of Real Estate Properties | property		3								3
China
Accounting policies
Number of Real Estate Properties | property		1								1
Income from rentals
Income from rentals
Revenues										$ 1,516,864	1,314,781	1,122,325
Other income
Income from rentals
Revenues										$ 14,432	12,678	5,772
Revenues subject to other accounting guidance
Accounting policies
Percentage of total revenues										4.10%
Income from rentals
Revenues										$ 63,200
Rental revenues
Income from rentals
Revenues											1,010,718	863,181
Tenant recoveries
Income from rentals
Revenues											$ 304,063	$ 259,144
Accounting Standards Update 2014-09 - Revenue from Contract with Customers | Income from rentals
Income from rentals
Revenues subject to the revenue recognition ASU										48,751
$2.2 billion unsecured senior line of credit
Accounting policies
Long-term Debt		$ 384,000								$ 384,000