Debt and Preferred Equity Investments - Narrative (Details)	6 Months Ended	12 Months Ended
Jun. 30, 2019 USD ($) loan segment	Dec. 31, 2018 USD ($) segment	Dec. 31, 2017 USD ($)
Preferred equity investment
Allowance for loan and lease losses, real estate	$ 1,750,000	$ 5,750,000	$ 0
Number of investments marketed for sale \| loan	1
Impaired financing receivable, with related allowance, unpaid principal balance	$ 145,100,000
Number of portfolio segments of financial receivables (segment) \| segment	1	1
Additional amount of financing receivables included in other assets	$ 87,200,000	$ 88,800,000
Recorded investment, nonaccrual status	$ 28,400,000
Weighted average risk rating		1.3
Mezzanine Loan
Preferred equity investment
Number of debt and equity investments not performing \| loan	1
Financing Receivables, Equal to Greater than 90 Days Past Due
Preferred equity investment
Recorded investment, past due	$ 0	$ 0

Debt And Equity Securities, Weighted Average Risk Rating

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Financing Receivable, Number Of investments Marketed For Sale

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Represents the number of portfolio segments of financing receivables.

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Represents the amount of financing receivables recorded in other assets on the entity's balance sheet.

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Number Of Debt And Equity Investments Not Performing

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- Definition

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 reserve to cover probable credit losses related to specifically identified fixed maturity real estate loans as well as probable credit losses inherent in the remainder of that loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 310
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82921503&loc=d3e21338-158488

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Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

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Recorded Investment in financing receivables that are past due at the balance sheet date.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

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Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
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