Significant Accounting Policies - Investments in Commercial Real Estate Properties (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Real Estate [Line Items]
Weighted average amortization period, above-market lease costs	5 years 1 month 6 days
Weighted average amortization period, below-market lease costs	14 years 3 months 18 days
Weighted average amortization period, in-place lease costs	3 years 9 months 18 days
Period from cessation of major construction activity to completion of construction project, maximum	1 year
Depreciation expense (including amortization of the capital lease asset)	$ 187,300,000	$ 277,500,000	$ 233,500,000
Amortization of above and below Market Leases	4,200,000	5,900,000	$ 4,500,000
Identified intangible assets (included in other assets):
Gross amount	199,722,000	215,673,000
Accumulated amortization	(182,643,000)	(190,523,000)
Net	17,079,000	25,150,000
Identified intangible liabilities (included in deferred revenue):
Gross amount	212,767,000	241,409,000
Accumulated amortization	(210,262,000)	(230,479,000)
Net	2,505,000	10,930,000
Net intangible assets reclassed to assets held for sale	1,800,000	0
Net intangible liabilities reclassed to liabilities relates to assets held for sale	0	$ 0
Other Identifiable Assets
Estimated annual amortization
2022	5,575,000
2023	5,409,000
2024	3,544,000
2025	2,027,000
2026	1,850,000
Acquired above-market leases, net of acquired below-market leases
Below Market Lease, Net, Amortization Income, Fiscal Year Maturity [Abstract]
2022	505,000
2023	476,000
2024	56,000
2025	234,000
2026	$ 205,000
Minimum | Above Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Minimum | Below Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Minimum | In Place Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	1 year
Maximum | Above Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	15 years
Maximum | Below Market Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	15 years
Maximum | In Place Leases
Real Estate [Line Items]
Estimated useful life of other intangible assets (in years)	15 years
Building (fee ownership)
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Building (leasehold interest) | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Right of use assets - financing leases | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years
Furniture and fixtures | Minimum
Real Estate [Line Items]
Estimated useful life (in years)	4 years
Furniture and fixtures | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	7 years
Building | Minimum
Real Estate [Line Items]
Estimated useful life (in years)	3 years
Building | Maximum
Real Estate [Line Items]
Estimated useful life (in years)	40 years