Fair Value Measurements - Additional Information (Details) - Property Funds [Member]	9 Months Ended
	Sep. 30, 2015 Investments
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of investments held by fund	3
Minimum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement anticipated investment holding period	1 year
Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement anticipated investment holding period	10 years