Real Estate Fund Investments - Summary of Property Funds Ownership Interests in These Funds and Funds Ownership Interest in Underlying Properties (Details)	Dec. 31, 2015
60 Wall Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
One Market Plaza [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
50 Beale Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
670 Broadway [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
Fund II [Member]
Investment Holdings [Line Items]
Property funds, percentage	10.00%
Fund II [Member] | 60 Wall Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	46.30%
Fund III [Member]
Investment Holdings [Line Items]
Property funds, percentage	3.10%
Fund III [Member] | 60 Wall Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	16.00%
Fund III [Member] | One Market Plaza [Member]
Investment Holdings [Line Items]
Property funds, percentage	2.00%
Fund VII and VII-H [Member]
Investment Holdings [Line Items]
Property funds, percentage	7.20%
Fund VII and VII-H [Member] | 50 Beale Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	42.80%
Fund VII and VII-H [Member] | 670 Broadway [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
Property Funds [Member] | 60 Wall Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	62.30%
Property Funds [Member] | One Market Plaza [Member]
Investment Holdings [Line Items]
Property funds, percentage	2.00%
Property Funds [Member] | 50 Beale Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	42.80%
Property Funds [Member] | 670 Broadway [Member]
Investment Holdings [Line Items]
Property funds, percentage	100.00%
Other Investors [Member] | 60 Wall Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	37.70%
Other Investors [Member] | One Market Plaza [Member]
Investment Holdings [Line Items]
Property funds, percentage	98.00%
Other Investors [Member] | 50 Beale Street [Member]
Investment Holdings [Line Items]
Property funds, percentage	57.20%