Real Estate Properties - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Real Estate Properties
Real estate property, gross	$ 7,824,763	$ 7,617,547
Real estate property - accumulated depreciation	1,454,477	1,270,716
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018	585,229
2019	567,632
2020	538,631
2021	517,541
2022	500,190
Thereafter	2,281,527
Land
Real Estate Properties
Real estate property, gross	824,879	792,728
Buildings and Improvements
Real Estate Properties
Real estate property, gross	6,675,516	6,519,145
Real estate property - accumulated depreciation	1,250,057	1,092,498
Furniture, fixtures and equipment
Real Estate Properties
Real estate property, gross	324,368	305,674
Real estate property - accumulated depreciation	$ 204,420	$ 178,218

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Future rental payments receivable within one year of the balance sheet date under an operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164653&loc=d3e41551-112718

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Future rental payments receivable within the fifth year from the balance sheet date under an operating lease.

+ References

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Future rental payments receivable within the fourth year from the balance sheet date under an operating lease.

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Future rental payments receivable within the third year from the balance sheet date under an operating lease.

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Future rental payments receivable within the second year from the balance sheet date under an operating lease.

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Future minimum lease payments receivable under operating leases for periods greater than five years following the balance sheet date.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
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Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-SubTopic 210
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