Acquired leases (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Acquired Below-Market Leases
Real Estate Properties [Line Items]
Amortization of intangible assets	$ 30,300	$ 22,300	$ 19,300
Weighted average amortization period	5 years 1 month 6 days
Values of acquired leases
Value of intangible assets, gross	$ 326,255	236,026
Accumulated amortization	(131,482)	(101,218)
Value of intangible assets, net	194,773	134,808
Estimated annual amortization
2020	44,269
2021	20,698
2022	19,503
2023	18,635
2024	16,940
Thereafter	74,728
Acquired-in-Place Leases
Real Estate Properties [Line Items]
Amortization of intangible assets	$ 49,100	34,300	$ 19,600
Weighted average amortization period	5 years 10 months 24 days
Values of acquired leases
Value of intangible assets, gross	$ 426,280	229,095
Accumulated amortization	(144,630)	(96,189)
Value of intangible assets, net	281,650	$ 132,906
Estimated annual amortization
2020	54,757
2021	49,878
2022	37,006
2023	31,885
2024	24,001
Thereafter	$ 84,123