Real Estate Fund Investments - Additional Information (Details) - ft² ft² in Millions	Jun. 30, 2017	Jan. 24, 2017	Dec. 31, 2016
Investment Holdings [Line Items]
Area of office and retail properties	11.8
Property Fund II [Member]
Investment Holdings [Line Items]
Percentage interest in fund	10.00%
Property Fund III [Member]
Investment Holdings [Line Items]
Percentage interest in fund	3.10%
Property Fund VII [Member]
Investment Holdings [Line Items]
Percentage interest in fund	7.50%
60 Wall Street [Member]
Investment Holdings [Line Items]
Percentage interest in fund			62.30%
Percentage remaining interest sold		37.70%
Area of office and retail properties		1.6	1.6
Property ownership, percentage		5.00%