Summary of Significant Accounting Policies - Basis of Presentation and Real Estate Properties (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 31, 2017 property	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Basis of Presentation
Ownership interest in subsidiaries (as a percent)		100.00%
Number of properties included in joint venture agreement | property	1
Total assets		$ 6,476,424	$ 6,653,826	$ 7,160,426
Liabilities		3,857,202	3,776,776
Increase in capitalized above and below market leases rental income		7,405	6,791	5,787
Amortization of acquired real estate leases and other intangible assets		$ 48,669	64,203	$ 72,925
Above market lease, weighted average amortization period, lease term		3 years 8 months 12 days
Lease, weighted average amortization period, lease term		7 years 4 months 24 days
Below market lease, weighted average amortization period, lease term		7 years 10 months 24 days
Finite lived intangible asset, future amortization
2021		$ 36,770
2022		32,959
2023		31,961
2024		27,108
2025		23,724
Thereafter		$ 66,161
Ownership interest in joint venture		55.00%
Variable Interest Entity, Primary Beneficiary
Basis of Presentation
Total assets		$ 970,142	1,015,661
Liabilities		$ 697,129	$ 704,344
Land and Building | Real Estate Investment | Maximum
Basis of Presentation
Estimated useful lives (up to)		40 years