Fair Value Measurements - Summary of Significant Unobservable Quantitative Inputs Utilized in Determining Fair Value of Investments (Details)	9 Months Ended	12 Months Ended
Sep. 30, 2015	Dec. 31, 2014
Property Funds [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates	7.00%
Property Funds [Member] \| Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates		6.50%
Terminal capitalization rates	5.00%	5.50%
Property Funds [Member] \| Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates		7.25%
Terminal capitalization rates	6.00%	6.00%
Property Funds [Member] \| Weighted average (based on fair value of investments) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Discount rates	7.00%	6.83%
Terminal capitalization rates	5.55%	5.72%
Alternative Investment Funds [Member] \| Minimum
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	7.32%	8.50%
Alternative Investment Funds [Member] \| Maximum
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	11.10%	14.00%
Alternative Investment Funds [Member] \| Weighted average (based on fair value of investments) [Member]
Fair Value Inputs Assets Quantitative Information [Line Items]
Preferred return	9.14%	11.07%

Fair value inputs preferred return.

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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.

+ References

No definition available.

+ Details

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- Definition

Ratio of the net operating income produced by an asset and its capital cost (original prices paid to buy the asset), used as an input to measure fair value.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

+ Details

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