Fair Value Measurements - Additional Information (Details) - 6 months ended Jun. 30, 2015 - Property Funds [Member] - Investments	Total
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Number of investments held by fund	3
Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement anticipated investment holding period	1 year
Maximum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value measurement anticipated investment holding period	10 years