Fair Value Measurements - Schedule of Fair Values of Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in Property Funds	$ 195,262	$ 183,216
Investments in Alternative Investment Funds	141,131	140,171
Total real estate fund investments	336,393	323,387
Marketable securities	20,365	20,159
Total assets	356,758	343,546
Interest rate swap liabilities	163,301	194,196
Total liabilities	163,301	194,196
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	20,365	20,159
Total assets	20,365	20,159
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest rate swap liabilities	163,301	194,196
Total liabilities	163,301	194,196
Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in Property Funds	195,262	183,216
Investments in Alternative Investment Funds	141,131	140,171
Total real estate fund investments	336,393	323,387
Total assets	$ 336,393	$ 323,387