Real Estate Fund Investments - Additional Information (Details)	9 Months Ended
Sep. 30, 2015 USD ($) ft²	Dec. 31, 2014 USD ($)
Investment Holdings [Line Items]
Aggregate committed capital	$ 580,200,000
Committed capital invested	$ 86,600,000
Area of office properties \| ft²	10,400,000
PGRESS and PGRESS-H
Investment Holdings [Line Items]
Redemption of preferred equity investment	$ 42,475,000
Realized gain on investment	7,455,000
Property Fund VIII
Investment Holdings [Line Items]
Mezzanine loans	86,813,000	$ 45,947,000
Property Fund VIII \| Second Mortgage \| Mezzanine Secured Loan
Investment Holdings [Line Items]
Mezzanine loans	$ 40,000,000
Area of office properties \| ft²	751,546
Loan maturity date	Oct. 31, 2019
Loan extension term	1 year
Subordinate to other debt	The loan is subordinate to $265,000,000 of other debt
Subordinate loan	$ 265,000,000
Property Fund VIII \| Second Mortgage \| Mezzanine Secured Loan \| London Interbank Offered Rate L I B O R
Investment Holdings [Line Items]
Basis spread on variable rate	6.00%

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Capital commitment invested.

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Description of subordination to additional loan

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Redemption of preferred equity investment.

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Area of a real estate property.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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

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Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes loans held for sale. Excludes loans and leases covered under loss sharing agreements.

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